T3s are drying up, but I've bought three at $450, $550, and $575. Yes, the T3 has an aluminum lug, but who's actually using that? Every chassis/aftermarket stock is going to have a steel lug anyways. If you buy a T3X, which most are doing, you have a steel shroud.
Tikka comes with a trigger that's good to go out of the box. I prefer my T3 trigger and $10 spring to my Bix'n Andy Tacsport. All the Origins I've tried I wasn't impressed with.
Does a Tikka compare favorably against a bighorn, yes. Does it compare favorably with my Lone Peak Fuzion, no. But like has been said earlier, an origin with a TT Special is going to cost you $1200, where a donor Tikka and trigger cost you anywhere from $500 to $800.
People touting that they're not in the same ballpark are just defending their spending decisions. My K525i still has CA and a narrow FOV, but it's European glass and costs over $3k, so it's obviously better than your mk5.