Here is probably what you are going to find. You might run across a new Suntour XC? (M, R or T) that is both, 80mm and can run rim brakes. In today's world both of those are tough to find. And, you will need to make sure you have a 1-1/8" steerer tube on your current bike. 80mm on your bike won't be an issue as in '94 bikes were designed to run 63mm and you're around a 20mm jump; which is what I am running.

There are used forks form that era, but parts are becoming extinct so you might get stuck with a fork that leaks and you can't get seals. I use Marzocchi bombers that are pretty bulletproof, but I might have problems getting seals; but I'm not up on parts for other 90's forks.

As for your knees, if they hurt because from peddling, then a suspension fork won't help. If they hurt because you get out of the saddle and use your legs as shock absorbers over bumps, then a front suspension fork will help maybe a little, but you probably need a full suspension bike.

The long and short of it, is that sadly there is probably no good solution for $150. You need to figure out what is hurting your knees and look for a more current fairly light bike with lower gearing, or full suspension, as upgrading your Iguana has to be more a labor of love than a low cost fix.

John