I don't know of any cheap new coin doors. They are all made of metal, at least as far as I know, so it's not like there's a cheap plastic consumer version or anything. They are easy to install, they're held on by clips. They are also easy to maintain. You might have to occassionally change the bulbs if you have your coin slots lit, but that's about it. Coin jams are easy to clear.
You can get used doors in good condition relatively cheap. As Peale posted, he was selling his used doors at good prices. You can also (sometimes) find good prices on eBay, usually better deals are in the mame and arcade newsgroups and on forums like this one.
You might want to rethink your token idea though. You can easily find used doors with working 25 cent mechs. If they aren't working you can buy new mechs at Happs for (I think) $8 or so. You won't need to "buy" quarters, but you will need to buy tokens, so that's an expense you wouldn't have if you went with regular mechs.