Baby steps, mate! Baby steps...... Hmmm..... let's do some maths:
8 x $50 each (that's IF I pay for them - my mate can do them as freebies for me, but I'll reciprocate in kegs of beer) - $400
8 x $20 covers for each one - $160
Plumbing fittings to stack/daisy-chain them all together - Guess @ $150
Total - $700 (ish)
By comparison:
https://www.bunnings.com.au/melro-8000l-poly-round-water-tank-merino_p0044281 That's JUST for the tank, no delivery fee, no site prep., no plumbing fittings.
No brainer, really......