One thing I'd also add is that if u can afford the little extra money upfront, its better long term budget-growing sense buying a good quality, brand name bloom nute & if poss, buy the next size up bottle to whatever you would buy for a few grows worth.
In terms of £ per L, Nute prices do often drop dramatically as you go up bottle size, and if u buy good quality and store it right then it can last perfectly fine for years and years. (Coolish, dry, dark cupboard and lightly shake every few months.)
For me, I only do 4 smallish, plants a time but I bought 2 x 1L bottles of grow/bloom about 2 years ago, used them on 4 grows and easily still got 1/2 to 2/3rds of each bottle left, which still looks fine for another few years of storage, though next time I'm gonna just buy 2 x 5L and be done for the next decade! And if ur talking double digit litres of nutes (which u lucky Yanks & Canadians probably are!), well it scales up relatively - the higher u go, the better the savings!
Tho admittedly it does mean investing in 1 brand for a long period too, so either research reviews or try samples first?!