To make your own All-in-One fertiliser and dose at the recommended 5ml/50litres would cost about 68p a year on a 100litre tank.
To run E.I. on the same tank would cost about £5.61.
Baring in mind that E.I. is for high light - co2 tanks - so to match that with an All-in-One you'd probably want to be using 3 or 4 times the dose....also E.I. is designed to be tweaked down to better suit your requirements, saving you money along the way. The added peace of mind with E.I. is probably priceless too....
HTH
(The prices are based on refill packs, so don't come in proper plastic containers and don't include postage)