Just try doing all the events in each area at least once and finding the coins, once you get the hand of it the acheivments will fly in.
Tip for getting Dr Butter and Like a top at the same time use a park board and hold the right stick about halfway in at the 2 o'clock position.
If your really looking for cheap gamerpoints, look out for an old copy of Colin McRae rally, think I've got about 960 points from that.
Oblivion gamerpoints are piss easy. Think i have 1250