Not quite sure what this has to do with Avis discount codes, but...

$76 all-in for Thrifty and Dollar looks to be about as cheap as it gets those days. You could always check their websites to see if there are any better deals, but most coupons and whatnot are for weekends, not mid-week rentals.

You can also try bidding on priceline a little cheaper than that. Try bidding for a full-size at around $22/day. That works out to about $63 all-in on PCLN. It'll probably be rejected, but I can't imagine you're going to get much cheaper than that for a mid-week rental.