Then armed with this you can at least see what area of shoes are relevant. Then you go in for a sneak try on in a shop and i hate to say it but if your broke then you go and buy em on the internet.
Sportsshoes.com as advertised on this site do decent last year models at half price or less and startfitness do the same, both quite often also have 10% off codes, sometimes these are added to the bargain thread. So keep an eye out there for these codes, so you can then get over £100 trainers for £40-50 is that cheap enough? If not then same principle do the water test decide what seems relevant and then hunt them out on ebay. Will take longer but might get a very slightly used real bargain.
I for example did the water test, found i over pronated, read some online reviews, and almost at random decided i liked the sound of the asics brand. So I went onto their website to see what trainers they recommended for over pronators.... Hey presto. I'm a big fan of going to shops to buy things as opposed to the net as we will end up with very empty high streets, but if you don't have the money, then needs must