To be honest the SJS tanks don't seem that badly priced given what's charged for other Lotus tanks, but if you can weld they're probably the easiest tank to DIY and you'll save a fair bit of the budget for stuff you can't do yourself. If you can weld and have a MIG set, then read on.
You can weld aluminium with a MIG welder, just use Al wire, Argon gas. Normally people on car forums think "TIG" for Aluminium but you don't need an A/C TIG set. Loads of aluminium is welded commercially with MIG, faster and much cheaper. As for the tanks, it's literally roll a sheet around a former and weld, slap on the end plates and you're 80% done. The tank with the sender is more complex but if you've got the first one made then you'll figure the second out, just a bit more welding.
I made mine in the 80s when there were literally none available anywhere, at any price. Not Lotus, Chris Neils, Spyder, none at all, the best I got was 2-3 months delivery. But it was my daily car so needed fixing PDQ. I can't recall how long it took but it was probably one of those weekend jobs, pull one out on Friday after work, hack a plywood former, weld it up for Sunday afternoon.
Still there, 35+yrs later..... but I do wish I'd fitted a larger bore crossover pipe, that was a slip-up.
