You must have really weird prices there, I get some really trusted and proven brand 99% iso for 6 euros a liter (if I would buy in 1l can) and the lacquer thinner is about 5 euros, so it makes little sense to use it. Maybe I'm not cleaning the board as others do and I'm on the cheap side but I'm not using one bottle per board at all. Probably the best thing I've ever done is putting an air filter before the intake fan, although I don't know for sure how effective it is as in how much goes through it (I know how much is captured, lol) and the fact that I have a ton of them around since we use those to prevent flour dust accumulation in the wheat mill.