There are numbers in life you never want to know, and this is one of those numbers. :lol
The most I've spent on a single kit was 700 euros. It was a big wooden ship - HMS Victory -- and I ended up dropping another 300 in some material replacement, upgrades and such.
Most I've spent on a single visit to a hobby shop: 1,400 Euros (1 wooden ship Frigate Diana & 32 different plastic kits for a star destroyer build)
Recently, I had to set up my new workshop with whatever I was going to need. I already had a vast collection of consumables and tooling, but there were still things I needed. Just in styrene I've spent over 600 euros (have almost all of the evergreen catalog from 100-297) and another 400 euros in silicon, resins, clear resin, body filler, epoxies, some new tools... OH and let's not forget the 400 euros for a Lexmark color laser printer and another 150 euros for a cutter, laminator, several packs of copper sheets and a few packs of 200#, 220#, 250# card stock.... Still gotta drop a couple grand to complete my workshop, but it's well worth it. Fun times.. :lol