Evict. They’re used to a free place to live, cash for keys won’t likely work.
@Account Closed is absolutely correct, offering cash means nothing to them. This tenant is a pro and knows how to use the system. Your best bet will be to HIRE AN ATTORNEY that specializes in landlord-tenant issues and evictions -get a specialist, not a general practitioner. It will likely cost about $500 + court costs.
My recommendation is to not worry about getting reimbursed through a judgment - it’s wasted time and effort. Just consider it part of the cost of the deal, your main concern is just getting them out as quickly as you can. Your purchase price should take into consideration the cost of eviction and subsequent renovation. If it’s a good deal it will be worth it.