Advice for a pup

This good boy is Henry Wolfgang. 8 years old this coming fall. Claims our kids as his own..
We brought him to the vet last Friday because he was getting chaffed and raw under his legs. He has had that before because of an allergy. We missed our first appointment 2 weeks ago because of the snow storm in NY.
We expected to have the area cleaned and another prescription. He's a chubby little monkey doing great losing weight too. His temp was 104 and the Doc said he has a massive infection.
They whisked him back and put him on an IV and antibiotics. We put $500 down for the initial care. Five days later he's off IV and the fever has been down without spiking. We are set to pick him up Friday. Bill is $3100 minus the $500.
Not something we were ready for because of other issues. We get $1000 but they want at least $2000 to release him. I understand. They did a lot for him. Coming up with the other $1000 is a big question. No one to borrow from and no way to get a loan. Looking for ideas 'cause I'm all out and we don't get paid for another 10 days.

Update: Henry is home and doing great. The Vet worked out a payment plan over the next 3 weeks.
Thanks for all the advice.