If you want to keep to the low-budget theme, you could find a low-cost small bus or motorhome model and paint it white, then apply some NASA stickers. It would not be a super-accurate model, but it would work!!
If you do, do not get a resin model - they are too hard to take apart and paint. Something like this would do nicely. Not sure if its diecast or plastic but it would come apart easily, paint nicely, and go back together with no hassle.
Here’s a Railking tank car from the 2010 V2 catalog. I’ve had it since 2011. My son was doing an internship at the Glen Research Center at the time so I pretty much had to get it. I usually run it with my smoking LOX tank car.