how much to pay for 7 1/4 sure grip and where to find one

I would love to put an 8 3/4 in my car but can't afford it.and 8 1/4 I'd need new rims

Anyway, my main goal is lower gears. First is it near impossible to get one with 3.23 gears and if you find one what is it worth and are all going to be sure grip if they have lower gears.
(i know a guy that has one but he doesn't want to get rid of it) so I'd it worth bugging him or can they be found possible on FABO and if he would sell it.what would be fair. I'm not too afraid of 7 1/4 as I've given mine hell for 4 years with no issues with a crate 360 ...

I just want a faster take off because that is more fun than cruising90 mph in these old cars