Lots of other good replies here.
I just managed to eradicate mice from a 2.1Ha predator fenced site by using classic wooden mouse traps (48c each from Bunnings warehouse – 140 of them) housed under recycled 3l plastic orange drink containers from our local recycling ctr, put through my bandsaw to leave a flat base from the mouse sized opening, and secured in place with a staple made from #8 wire bent to shape by hand.
Took me about 300 hours over 4 months but cash outlay was under $300 (including replacing a bandsaw blade). Had 117 traps at peak (quite a few failures, but relatively low rate in the grand scheme of things), 250 mice caught in total, 23 on the peak night. 3 jars of Pics peanut butter used.
Using clear plastic bottles means checking traps is quick, just a glance tells you if they have been set off.
Bycatch was minimal (3 skinks and about a dozen snails).
Ants were an issue in some places, but borax sugar mixture in old beer-bottle tops solved that – only about 10% of trap sites had the issue.
Near the end had one blackbird figure out how to get a free feed of peanut butter, but it wasn’t an issue overall. It only happened because I hadn’t flattened that trap site well enough, and there was a small depression allowing the blackbird to get under the plastic and worry away at the trap until it work it out from under the cover (got trailcam footage of it performing this trick).
As others say, depends what you want to get, and how much you value your time ;), and how much you want rid of whatever you are trapping.