Free: Contests & Raffles.
I run a CMC trigger in my mega Maten. I really like it and it won't break the bank.I have a couple CMC triggers in AR's and they've been great so far, no complaints. There's a lot of really good drop in triggers for AR's out there so it'll somewhat depend on how much you want to spend but for a good trigger that won't cost you a lot, the CMC triggers work well for me.