Fairly rare to pop up for sale but the value has dropped over the years, you can get them for about £40-50 now. They would fetch £100 about 5 years ago.
I wouldn't bother changing them unless they are in bad/ugly condition. I fitted brand new ones to my forged build as the old ones looked fairly rusty. Personally I would only use OEM replacements. We have them on our website should you decide to change them.
It belonged to 'Newbe', a member on here from Leeds. He had a few years and it did a fair few aftermarket parts but he returned it to almost stock when it came to selling it. I can't find his build thread but here's his profile: Click I am 99% sure this is his old car.
6.5" are the most common. Iirc they come in ET32 and ET38 (or 40, can't quite remember). The 32s are more rare and have a deeper dish, so obviously they look epic! I've never seen 7Js?