I come from Android and have to say prefer I4 I have had milestone, Desire and Galaxy S.
If you going to android i would say Desire or Galaxy S seem to be the best choices out, from personal experience i would take the Galaxy S over the Desire but that will still cost you close to ?400.
Desire seems to have dropped in price a bit and i seen it sim free for ?379 mark so a decent price there.
Other option is say the HTC Wildfire which seems to go around ?220-?300 mark. Wildfire below.
http://www.youtube.com/watch?v=FCU30xyiqAQ
I don't think you will get much for ?100-?200 unless you look for second hand or maybe a HTC Hero ?.