"Cash for keys" is a deal that the new owner might offer you to vacate the premises without a lawsuit. It is not a right.
If you're on a month-to-month tenancy, as long as you pay your rent, the new owner can't terminate your lease without giving you a prior 90-day notice.
I have to assume that the 3-day notice is for violation of a term in the lease including failure to pay rent. Otherwise, it is not valid to terminate your lease for reason stated above.
If you have a lease, the new owner must honor the lease unless s/he wants to move in as his/her residence. If the new owner wants to move in or if you are renting month-to-month, the new owner must give you at least 90 days written notice to move out.
This is not legal advice and does not create an attorney-client relationship. The information about is a general statement of the law. Reviewing a case and giving legal advice to a client requires more information than can be exchanged in this format. If you need legal advice, contact an experienced tenants' attorney.