I just sold an SLX Paramount frameset w/DA headset for $285 with free shipping, new paint and decals from the maker. Market is down, or I just didn't have patience. It had a very small post-paint dent on the L upper fork above the frame decal. Maybe that was it, but I bought a set of carbon Race XXX Lite wheels with tires, and needed to replenish the funds....

I think you would be well served at a budget of $500 to include a headset, and go from there, adjust up for extras, down for work needed. I'm aware of deals in the last year or so....$225 SLX frame/fork needing paint/$400 SLX frame/fork needing rubbing out/waxing, but with some extras/$625 SLX frame/fork/headset ready to go/$285 SLX frame/fork/headset w/small dent on fork (mine above).

Bear in mind, once you get one, just build it and ride it with confidence. It's yours, and will be as good as you want it to be.