Looking for ideas - Decent cheap 26" 1 1/8" suspension fork for 1996 Trek 950 mountain bike Goal: 

Replace rigid fork with short-travel suspension fork for under $200 (used OK, switching to threadless from threaded OK; standard 100mm QR axle preferred but 15mmx100 through axle OK; V-brake mounting bosses preferred but disk-brake-only OK)

Seems like short travel (e.g. 60mm) will be needed to fit A2C; has low-end fork suspension technology advanced enough that a recent cheap air shock would be better than a 15+ year old used fork like maybe a Judy?

My bike:

1996 Trek 950 mountain bike; 26" wheels, cro-moly frame, original rigid chrome fork using 1 1/8" threaded headset.
Trek tech manual says geometry is designed for axle-to-crown race (A2C) distance of 408-430mm, but I would be OK with up to 440mm.
Tech manual link: http://www.vintage-trek.com/Trek-Fisher-Klein-Lemond/1996specmanualTrek.pdf
Bikepedia link: https://www.bikepedia.com/QuickBike/BikeSpecs.aspx?item=50637
Honestly, it seems that you want too much of everything at the same time: cheap, good, compatible with your depreciated frame suspension fork. You might reconsider your constraints.


Compatibility comes first, otherwise there is not much sense in getting a new fork. You'll need something for 26" wheels and with a straight 1⅛" steering tube, which is not what modern forks offer. I would say the majority of aftermarket suspension forks are for 27.5" or 29" wheels and likely to have a tapered 1⅛" - 1½" steering tube.


Then you have two remaining exclusive options in the requirements space.


Cheap — find a new OEM fork for entry-level bikes. There are decent chances to find something for 26" wheels, with V-brakes and straight steering tube. But such a fork is not likely to turn out to be "good" in terms of suspension performance and longevity.
Good. Go for a hunt on vintage market or consider having a modern fork with all mandatory upgrades it brings with it. Neither option would be cheap. For example, a new MRP Loop SL for 26" and straight steering tube costs USD 800+. Add to the price the front wheel change (through axle), front bake change (disc brakes).


Yet, finding a used old fork still looks more promising, and there is always a chance to find a deal.

On the last compatibility note, the 60 mm of travel is something not commonly seen for MTB these days, even on entry level forks. There is e.g. Lauf Carbonara gravel 
fork, but it is not something you'll want; besides, it is not straight steerer neither for 26" wheels.