There is no business "license" requirement in PA. Depending on organization of the business, either as a corporation, LLC, or simply registering a ficticious name, the costs vary. You may consider going to www.dos.state.pa.us for more information relevant to the study of entrepeneurial enterprises in PA.
Allow me to add a bit to the first attorney's answer: although there is no generic "business license" in PA and your startup costs would include whatever form you chose for your enterprise (corporation, limited liability company, partnership, sole proprietorship) and whether you would have to register a fictitious name, local governments in PA have their own requirements for doing business. For instance, depending on how you chose to market and distribute your product, you would have to check local requirements for operating a business (are you renting office space or operating out of your home?), and you may have to check the zoning requirements and obtain a variance if necessary. That's a time-consuming process.
Also, depending on what you would be doing, local governments require individual business licenses for certain businesses that operate in their jurisdiction. You also would have to obtain a sales tax license from the Department of Revenue.
My recommendation to research costs would be twofold: first, go to the PA Department of State Corporation Bureau website (http://www.dos.state.pa.us/portal/server.pt/community/corporations/12457/general_information/571896) and look at the various forms and information available there. Make sure you do a name search to find out if the name you want to use would be available. Also, there's a "PA Open for Business" website (www.paopenforbusiness.state.pa.us) that has all sorts of information about startups. I'd highly recommend you start there.
Of course, as with all of my online answers, my advice is limited by the brevity of your question and the facts provided. Additional information would be required to provide definitive legal advice, so this answer isn't intended to, and does not, create an attorney-client relationship.
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