I would accept $2000 but maybe put it as $2000 (and something) and go for ONO. Depends on the muffler too.. why is it loud? Does it have a hole? A new muffler/exhaust system can be quite pricey to replace if you cant do it yourself.

Looking around... The pretty decent knick ones are going for about $3999, so if its $600 to fix, why not do it yourself and then you can ask for more for it? Rego usually isnt an issue for people but most of the time when they are looking for a car, its because they actually want to buy it to drive, not have to have it in the shop for weeks getting fixed IYKWIM.