I don't known what the Gelert and Wynnsters tents are like, but owning a sub £100 Vango tent (Micro 200) then I can certainly vouch for their quality.
Even cheap Vango tents show well thought out design and quality, from loads of internal popckets, the quality of the poles and pegs, to the general finish.
Having said that, I also have a four man EasyCamp tent for £45 for camping with my girlfriend (who is claustophobic so will only go in cavernous tents), and that was quite good - for the money. Nowhere near the quality of a Vango though.
Like all things, you pay your money etc. But if you want to get reasonable life from your tent I would highly recommend Vangos.