i agree you can build a cheaper pin than bying one, but you'll have to make compromises.
and the cool pinball parts like a VUK (100 euro), autoplunger (140 euro), ball through (150 euro), flipper assembly (50 Euros) just cost their money.
also i always under estimate the cost of all the cables you'll need.

my first homebrew cost me around 4200 euros, bought lockbar and coindoor all new and made the cabinet new.
on my second i used lots of parts from an old EM machine. but flipper assembly parts backfired on me. new technology works just better with all that forces.
so my second came in at about 3000 euros.

i did however save money on posts, plastics, inserts and walls, because i 3d printed them.