If your patented invention is being infringed by a big company, I would think that the damages are big enough and liability is clear enough for you to be able to find an IP litigator on a contingency basis.
If you already spoken to many lawyers and none of them will take your case, then either the damages aren't as significant as you imply, or the liabiity isn't as clear as you think it is, or both.
No one on Avvo can assess the merits of your case, you need to consult lawyers face to face with your patented invention and the allegedly infringing product.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
Patent infringement litigation is often intense, complicated in both the legal subject matter and technical subject matter, and always expensive. (One to five million dollars in legal fees is the average cost to litigate a patent infringement dispute). Depending on where a suit is filed it could take anywhere from 1 to 4 or more years to reach trial. (Assuming the accused infringer does not put the patent into a reexamination and obtain a stay of a district court action during the suit). There is always the possiblity of an appeal to the Federal Circuit which can add another year or more to the final resolution.
Some firms are willing to handle patent litigation on a contingency basis, but many find the risks to great.
If you have not been able to find a law firm willing to handle the matter on a contingency basis, you may want to consider selling the patent to a firm that is in the business of buying patents to enforce, such as Acacia. Most likely such a firm would give you a share of any damages if a suit was successful but only after subtracting their expenses. Hence, IF your patent is valid, enforceable, and infringed, you would receive some money under the arrangement, but not as much as you would if you could personally enforce the patent. If the lawsuit is not successful you would probably net nothing from the sale.
If the alleged infringer has competitors you could always explore the possiblity of selling the patent to a competitor and let them enforce the patent. Potentially, you might be able to sell the patent for a fixed sum plus a share in any recovery from enforcement. If you are the inventor you will be involved as a witness in any suit to enforce the patent, whether you want to or not. So any entity purchasing the patent would also want to obtain your cooperation in any suit to enforce the patent, which could give you some bargaining leverage.
Patent infringement litigation is challenging to even the experienced lawyers. Only a fool seeks to enforce a patent pro se (i.e., without a lawyer experienced in patent litigation).
There are many reasons why a patent cannot be successfully enforced. Hence, I do not, and cannot, address your personal situtation, including whether any buyers would or should be interested in your patent.
Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.
Additionally, I am providing this as a public service courtesy to the questioner and the Avvo community. I do not handle contingency matters.
The one suggestion that I might make is this: You should take evidence of the infringement to the law firm that originally helped you obtain the patent on your product and find out the terms on which they are willing to handle a claim for patent infringement.
Assuming they handle litigation as well as patent prosecution, they are in the best position to know the strengths and weaknesses of the patent and the ability to succeed on infringement claims. They would be in the best position to handle it on a contingency fee basis. If they are unwilling, it is unlikely that you would find another litigator who would. Good luck.
Disclaimer: According to AVVO's Rules, this answer does not establish an attorney-client relationship nor constitute legal advice. It is for general informational purposes only.
Great answers were already given -- in short, because you cannot afford to file suit you could (1) try to find litigation counsel who will take the case on contingency, (2) sell your patent to a patent holding company or to a competitor of the alleged infringer, or (3) do nothing. That's the universe of your options.
You should NOT write your own cease and desist letter -- or even contact the alleged infringer -- because either may very likely trigger its right to sue YOU for a declaration that what it's selling does not infringe the patent you say is infringed. That lawsuit will also ask that the court declare your patent is invalid. You will have to defend that lawsuit or else the "huge company" will win by default and you may lose your patent. So restrain yourself from contacting the alleged infringer -- and from making any public comment on the subject via blogs, newsgroups, facebook, etc.
One loose end: you say the alleged infringer has "repackaged" your product and is selling it. Does that mean you're currently selling the product that's covered by your patent? If so, is the product marked with your patent number and/or the brand name that you chose to sell it under? If either, is the "huge company" simply re-selling your marked product as is, or is it stripping off the patent and/or branding markings? If any of these things are happening your odds of finding contingency fee counsel to take the case go up dramatically.
But if you simply believe that someone is selling a product that infringes your patent then you will have [as my colleagues have noted] a much more difficult time persuading contingency fee counsel to help you.
One last thing. Many times consumer products are manufactured overseas and imported for sale. If the alleged infringer is importing the product you say infringes your patent then you can [only with your attorney's assistance] report the alleged infringement to Customs and Border Protection. See https://apps.cbp.gov/eallegations .