If your scope budget is $300, I would get Cast to do the cheap trigger job and bump up that scope budget every bit you can.

I had a Bill Springfield trigger job done on a DPMS AR-15 for around $40-$50 IIRC, and it was night and day difference from the factory trigger. Almost as good as the stock Rock River trigger on my 2nd AR. Rock River has the best factory trigger out there in the sub-$1500 market IMHO. And you should improve the trigger if you want to improve accuracy. It's worth the relatively small cost.

I'd get the good QD mount and the best 1-4 or 1.5-6 scope you can afford.

I agree with patriot on this, even though I love my Geissele. If you can get a nice trigger job for cheap, put that extra money towards the glass. You'll be happy you did. Buy right, cry once.

Agree on the LaRue QD scope mounts and the VTAC sling.

Love my CMC trigger. Well worth the money.