My build.....AR build anyways.
It's supposedly the cheaper route to go. I didn't do it for the money but right now I have about 200 wrapped up in the lower and lower parts kit which includes the trigger.
Ther were lowers there as cheap as 70 bucks and you can find them for much lower.
I wanted to build a good rifle without breaking the bank so I plan on ordering my parts from manufactures I know but still not buy the top of the line stuff.
manufacturers (of guns) have to pay an excise tax on any assembled firearm sold, it's in excess of 10% - so building it yourself saves you that right off the top.
Cheap parts are a gamble: go with known/trusted names when it comes to cheap. Aero Precision, PSA (Palmetto state) and Anderson arms come to mind. Don't expect a $40 lower to be perfect - but all three of those companies have okay-ish track records when it comes to customer service. No-name shills at a gun show peddling $50 lowers won't do anything for you when you find out your buffer tube is crooked, or your fire control pin holes are out of spec.
The three things that shouldn't be skimped on are barrels, carrier groups, and the fire-control group (trigger, hammer, et. al.). Buy a reasonable parts kit ($100 or more, typically), a good carrier (they're really as simple as they look, quality especially matters here), and a barrel from a reputable supplier. PSA makes some OK stuff that's very cheap (relatively), but it's hit and miss. Some are good, some aren't. If you're building a plinker they're usually just fine. If you're building a hunting weapon or something that will be used as home defense or any 'duty' roll, I'd buy-up.
~$200 into an assembled lower isn't bad. That's on the 'budget friendly' side of things for sure.