Actually I looked up all the parts with buying a used JG, Echo1, CYMA, AGM, or UTG M14 and even with trashing the original gerabox and it's internals the total build was less than $500. That's buying the gun, tightbore, G&P reinforced 7mm geabox shell, gears, spring guide, tappet plate, cylinder, piston, piston head, cylinder head, o-ring air nozzle, spring, and high torque motor. In my experience, your barrel and airseal are THE most important parts in a DMR. Remember theat consistancy is the key to accuracy and the better your air seal is the more consistant you'll be. I haven't got to try one out yet, but I've been refered to using bore-up kits for DMRs that way you don't have the NEED for high torque gears and motors. Also the Bore up kit makes your internals last allot longer in that you can get the same velocity as an upgraded gearbox with a stong spring (m125+) while using only say an M120. I personally have 2x DMRs and both of them are worth taking onto the field and always pay off.
In my experiences a spring sniper is always the most expensive gun to make it worth taking out onto the field. All the really good snipers I've met and play with say the better sniper rifles are always around $1000 or more.