If you believe you can, or you believe you can't... you're right.
Michael W. Graves
If it ain't broke....don't fix it!
No problem. You should be able to find a 90 well within your price range. I picked up a Schneider 5.6 90 a few years ago for $200 in a well-operating shutter. The filter ring has a ding but all is OK with it. Personally... I don't like the lens or the 90 FL on 4x5 and got much more for my money, and greater utility, with longer (12 inch/ 300 mm) FL lens. I'm not a WA kind of visionary.
Maybe this is the wrong place to post this... but I have a nearly mint 90mm SA f/8 I want to sell. I want a tad more coverage so I'm replacing it with a Nikkor SW f/8. I don't want to sell it too cheaply but I'm realistic about it's current value. Anyone is welcome to chime in regarding how much I should ask for it. I can post pics here if you're interested.
I've just bought a 90mm SA f8 in Synchro Compur shutter from a dealer in the UK lens and shutter are exc++ and I paid £249 uk.
As already mentioned you could go for a cheap 90mm 5.6 Angulon, but you may prefer a 90 with a larger image circle so that there is more scope for movement. I think it worth paying a little more for a Super Angulon personally if you want a 90mm lens.