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Weird one. Most movies don't have budget listings on IMDb, especially low budget ones. Also, a million dollars got you a lot more if you made your film in Italy, or in the 1940s.

These are all of my 4.5-5 star movies that I've managed to find the budget for, combined with those that are well known to be micro-budget films, with those most in the spirit of the thing towards the top-10. A whole bunch of for-sure sub-$1M movies are missing though, especially "foreign" titles.