Pay it off
It’s very logical that they refused your pay-for-delete for $80. According to the The Fair Credit Reporting Act (FCRA), deleting an account from their report to the credit bureaus is illegal. By doing so, they risk their relationship with the credit bureaus.
It’s not that PFD agreements aren’t practiced. Some collection agencies will agree, others won’t. But no collection agency will risk their relationship with the credit bureaus for $80!
Those that are willing to risk it will probably only consider PFD for a minimum $1000 – $1500.
As for your question – Pay it off. It’s only $80! It should have never gone to collection in the first place! The damage you’ll do to your credit will (or already have) cost you much more than those $80.
Not that paying off will raise your score. It won’t. But a paid account will look much better to potential creditors when the review your account.
For more information on pay for delete see pay-for-delete.html.