Christmas week in London - easiest footbal tickets to get?

I will be there (on holiday from the U.S.) the week between Christmas and New Years, and find it almost impossible to get tickets for a match ahead of time, but don't want to risk waiting until the day of the match. Prem or Championship, any teams, and I don't want to spend more than maybe 50 or 75 quid a ticket. Do I have to be a "member" or something?