Mostly time and the wife's patience
the metal tube for the barrel was a $5 table leg from Ikea but you can alternatively use PVC electrical tube (I have some spare if you want it... cost me $6 for enough pipe to make 9 blasters)
Paint is mostly the cheap Australian Export stuff from SuperCheapAuto mostly (4 cans for $10). I've used the Gray Primer, Gloss Black, Satin Black and Chrome on this. I did splurge though on a Hammerite Hammered Black paint at $18ish from Masters as I like the finish
The resin pipe build kit from doopydoos.com is UK pounds 25.99 ... (you can get a complete kit which includes a pipe as well for UK pounds 37.99) the one i have doesnt include a scope, counter, power cylinders or T-track though
The spring was US$10
Scope rail is a $5 3mm strip of aluminium from Bunnings cut and bent
the scope - about $87 posted from US
so only prices I don't remember at the moment are
the counter - over $100
the power cylinders - kit from a US member off whitearmor.net $20-30ish?
the t-track - ordered from UK member off whitearmor.net