Don't forget to factor in the 'kewl' bits for a DMR... scope, bi-pod, and kit you'll need like a decent battery & charger, mags, BB's and kit to wear and carry mags etc...
A lot of rif's are great out of the box so save upgrades until they're needed.
Not sure about many other sites but my local site classes all rifs as select fire unless it's a bolt action and max fps for non bolt actions is 360 so your 450 fps might be an issue.