i wouldnt bother with any samsung galaxys phone other than the i9000 which is very easy to root and modify, check on XDA developers to check if other galaxy s phones can be rooted, variants of the i9000 from the US can be , and also the korean m110s but thats a nightmare for custom roms as it uses slighty different hardware...
Alot of older htc phones are very Root friendly, including the magic 4-5k, Hero 7-9k and the legend 11-13k, also the desire 14-15k and the nexus-one all the way up to the desire-hd 20k+
Zte do a great android phone Zte Blade or branded as the orange sanfranciso in europe it has a 600mhz cpu same as the legend so adreno 200 gpu performance, overclock to 768mhz , older ones have a amoled screen 3.5inch
also old htc wildfire is around 7-8k bnew
also check out the Meizu m9 from china, its a brillant phone with same cpu and gpu as the samsung i9000 plus a Qhd scree 960x540 aka same as iphone resolution and 3.5 inches - not sure thats rootable yet and its a little expensive
hmmmmm decisions decisions