Need advice on finding value on a '74 Mustang.

Here's my problem.  My mom and 2 siblings were left a 1974 yellow convertable Mustang that's been garage kept with less than 1000 original miles on it.  It was their dad's originally. My uncle has it now and I'm afraid he's going to snowball my aunt and mom about a price for it.  The girls want to sell it for the money and he acts like he's for that but has mentioned to a mutual friend that it's not leaving his family.  What is the best way to find a fair assessment of the value on their car?  He works in the auto repair industry so I'm afraid he'll get a friend to give an appraisal that would be in his favor.  Are there any ways to get an honest appraisal?  I can try to find more specifics about the car if possible.  Please help?  

I didn't think they made a convertible in 74, it must be rare.  

It's probably a '73 then because it's not a Mustang II and it is a convertable.  My dad thinks it has less than 500 miles.  I saw a '74 with 60,000 miles for like $800 on ebay but this has to be more.  

I'm a huge mustang fan and I have to say mustang 2s suck. I guess they are no worse than any other late 70s cars though (front suspension is great) I cant believe a 302 could have less than 150hp (low compression). I stand corrected I owned a 87 bronco 2 for a while 2.9 with death rattles. A 73 can fetch some coin depending on options and maybe because its the last year for a drop top till 84? The last year of a body style can mean something. The fact that it has low miles is good as long as its confirmed. I would throw it on ebay if you dont want to keep it.  

i heard somewhere that some shops were turning stock mustang coupes into convertibles, but if i remember correctly that was in 1980 and they were really poorly made. but hey, stangracer, the mustang 2s didn't really suck. to quote MM, they are infinitely better than the 03-08 camaros produced. hey RissJim, it would be really great if you could post a pic of the car