I would start somewhere between the Colt and a Daniel Defense. 3 gun isn't so much about sub MOA accuracy as it is about reliability. Holding 2 minute shots out to 300 yards will put you in the running. Having to clear a malf part way through your run will throw you off for the rest of it...
Scopes.. if your budget is tight, a lot can be done with something like the Vortex Strike Eagle 1-6. Next step up would be the Vortex 1-4x24 PST. Ok, ok, i may have a tendency towards Vortex. I just feel it is a good compromise for the money.
I havent had a lot of time behind the Trijicon but it didn't suit my fancy not being able to call my hold over past 200 yards. I'm sure with some practice a guy could figure it out. If I was only shooting inside of 200 yards I would try one out, probably on a shorty rifle.
Edit: just to give an idea on costs. A DDM4 V11 with a Vortex PST 1-4x24, ADM Scout mount, 3 Beo mags and a VTAC sling would put you right around $3000 total.