I've been using mapwindows gis for a lot of my needs, but I have a new challenge that I need a solution for:

I'd like to overlay block level census data onto political districts and assign the data from the best fitting census block onto the political district. This way I can have a rough estimate of the demographics of each small political district. What types of gis tools do I need to do this? I'd prefer it to be gui based and cheap (under $3-400) or free. Thanks in advance for the help.