I don't think your generalizations on what is high end versus low end are very accurate. I would say a PSL is low end, but not a Dragunov. A real Dragunov will cost you more than just about any other rifle in the DMR category, and most are MOA accurate with Russian sniper ammo. Another option in that category would be the Zastava M-76, which is basically a PSL type rifle in 8mm Mauser. For other eastern bloc rifles that could serve the purpose, you might look at a Saiga .308 for a solid low-end choice, or a Vepr/Vepr II for a higher quality Russian .308.
It is also not accurate to lump all .308 AR rifles together as "middle price." You have low-end ones like the RRA LAR-8, Bushmaster 308, and DPMS LR-308, you have true middle of the pack ones like Armalite's AR-10, CMMG's .308, and some of the higher end DPMS', and you have the real high end ones like the LaRue OBR, LRWC REPR, LMT 308 MWS (the current British DMR), Georgia Precision GAP-10, KAC SR-25 and M-110 (one of the US military's current DMRs), and the FN SCAR 17 (which is in use with SOCOM).
You mentioned the M-21 (there are actually several M-14 variants that go by that name), but there are other versions of the M-14 platform you might consider. Any of them are going to be accurate enough to fill the DMR role. Look at all the offerings from Springfield Armory Inc., Fulton, LRB, 7.62mm Firearms, and Smith Enterprises. Also consider an older Springfield, Federal Ordnance, or even a Chinese Norinco or Polytech for a low-end version. FYI one of the US Army's DMRs is a GI-barreled M-14 in a Sage EBR stock.
I suppose if you want to consider all your options, you might look at some of the G-3 based platforms... they can go from real low end like a CETME or a Federal, to middle pack like a PTR, or high end like an HK. There are real high end ones called the MSG-90 and PSG-1.
A FAL could serve as a DMR. Most are low to medium end, but DSA makes a more high-end DMR oriented model with fully adjustable stock and all that.
A Saiga .308 is a good low-end choice.
Also don't forget that the military uses some 5.56 rifles in the DMR role. One of those is certainly capable of taking care of business at DMR ranges, especially with some heavier rounds. You probably want at least an 18" barrel for that role. That is what the Army uses on their SPR's. But there are so many options when it comes to building 5.56 ARs that I'm not going to even get into it.
Hopefully this at least gives you some possibilities to look into!
