[84LX89GT]

I think you priced it right to be ACTUALLY able to sell it. I see people do that all the time, and when you've modified a car it usually means these things (not necessarily, but there is a MUCH higher chance):
1. That it has likely been abused more than a stock vehicle
2. There may be problems associated with the modifications
3. there's no telling how well it was modified (procedures, quality of install and parts) and if things will blow up after short usage.
4. the person knew enough to modify the car, so they know enough to cover up any flaws that will show up down the road.
5. There is a lower demand in the general car market for a modified vehicle because of stated reasons.

You can sell anything at any price, you just have to find someone that will be willing to pay that price for it.

For your Mach 1, since it was modified i'd say 6,000 was a very good price for a modified car because a Stock original version of your car would probably go for 10,000 just because it isn't as molested and changed (for good or worse).

.....i always laugh when i see lifted Chevy 4x4 truck owners asking 10,000 for any 80's or earlier truck....when you take garbage and jack it up 3 feet, it just means it'll topple farther.