You have to be more specific -- a film camera or a digital camera? Do you need a 35mm print in the end to show on a big screen? Can you afford to shoot Super-16 or 35mm? Can you afford to transfer anything digital to 35mm for a feature? Typical laser recorder transfer of anything digital to 35mm interneg for printing on a feature-length project is around $50,000 or so. Or did you just want to finish to HD and project digitally?
How do you define "decent"? One person will say that 24P/480 from a DVX100 looks "decent" on the big screen while another will say that 24P/1080 from a Sony F900 HDCAM looks like crap on the big screen. Quality is a personal judgement call that only you can make.
Asking for "cheapest" but "looks decent" is rather like the oxymoron of wanting "cheap and best". There are 24P DV cameras like the DVX100 in the under $4000 range. There are 24P consumer HD cameras in the under $10,000 range. There are also some basic (older) 16mm sync-sound cameras in that price range too.
