Vote with your wallet and ask an amount of money that will make up for the nightmare. I don't mind working on shit if I am compensated well enough that I only have to endure it for a couple weeks to be able to take a long holiday.
If they decline, leave for greener pastures. The market will eventually fix it; the high turnover will force the company to either pay more or fix the problems with the code base so they don't have to pay insane amounts of money to retain talent.
Identify why you dread looking at it and address that head on. It could be personal, it could be a monolithic mess, it could be no comments, etc. and there are strategies for dealing with them, alternatively a new job.
If they decline, leave for greener pastures. The market will eventually fix it; the high turnover will force the company to either pay more or fix the problems with the code base so they don't have to pay insane amounts of money to retain talent.