I dunno, I very recently priced a custom low profile tank for our garage and it was almost 3000GBP. I Checked around a bit and saw similar pricing in Germany too, ended up going for an off the shelf 350 baffled tank as below. I am also going to make some assumptions that an the shelf tanks from a reputable manufacture is going to be more reliable, better quality and hence less risky than a custom made unit (probably using cheaper and lower grade tooling on much smaller scale).. Assumptions..