It is not hard to get, people just realize they miss out on more, if they overspend on a PSU and as are forced to get worse components because of it.
I personally had to choose between a modular PSU and a bigger SSD. Though I did give it some thought, in the end I realized that the convenience of a modular PSU doesn't outweigh the necessity of a bigger hard drive (the damn thing is already full -.-).

Not to say that the OP overspent on the PSU, but as long as your PSU has at least bronze certificate, the wattage you require and, if possible, with at least one professional review, then it is a reasonable choice for your computer. Anything beyond that is a more a matter of convenience and not necessity (there are obviously exceptions. If you need a quite PC, you'll get a quite/passive PSU etc.).
Looking at the OPs setup he needs a 500W PSU (as long as he doesn't overclock) and as such reasonable PSU choices start at roughly £50, which is considerably less than 1/15th of the build price you suggest. For £80 he could get a semi-passive, gold certified, modular 650W PSU with an excellent review to top it all off, a price that still away from the 1/15th of the total build cost (if we don't count the screen in the cost, it just reaches 1/15th of the price).