I'd take the money and run if you don't think there is much damage. If you take the money, will they consider it totalled? If not, and you aare keeping the car, put it on ebay for $400 with no reserve and pickup only for shipping. Might be a way to make up the difference between the $4000 it'* worth and the $3000 they are offering.
If you know there is most likely mechanical damage, then you might be better off trying to get it fixed, but ask that they pay the full towing and storage expense.
2007 Saturn Aura XR | 1970 Chevy Blazer 4x4 | 1970 GMC 3/4 Suburban 4x4