I like the 516 Precision Marksman... Looks like a more affordable option than building an SPR - it's like $1500 for a BCM Mk 12 upper, figure then around $4-$500 for the lower and parts kit, the Magpul DMR stock, upgraded pistol grip, etc.
Obviously the BCM Mk 12 will be more popular but the 516 PM looks pretty effective, just my humble opinion.