You get what you pay for in a seat. It's an area you do not want to buy based on price. If you're not comfortable while driving it won't matter how much you like anything else about the car. A bad seat will ruin the whole experience for you.
You will never do better than a major manufacturer OEM seat. Every single piece on them has to pass pretty stringent safety, quality and wear testing. You might be surprised how relatively inexpensively you can grab a good set of seats and have them recovered as compared to buying an off the shelf, one size fits almost all aftermarket seat. The Fiero seats I used the mustang, for example, fit perfect in our cars. You can still find a pair of them for around $200-300. The big thing on seats for the old mustangs is getting the seating height dimensions right. Far too many choices I've seen people make just don't look right as they sit too high in the seat bottom making the top of the headrests WAY too high and make the side view look just wrong. You can find plenty of examples on the internet. I myself picked up a beautiful pair of BMW full power leather buckets I intended to use in my truck. Spent a lot of time finding just the right set. Did my homework with measurements and all and thought I had a winner. After MUCH fabrication...and refabrications...I found there was just not a way to get them to sit at the right height and placement in the cab to suit my desired driving position and look correct. While I could have used them and lived with it, I would never have been happy with either the comfort or look. So off they went!
TMI does a good job of sizing their seats to fit the older classic cars. Their seat frames are well made as well. I am using a bench seat from them in my F1. I can't really say I have found anything I dislike about the way it is made or the quality of the materials.