There is an active community of people dedicated to collecting, repairing, and restoring classic arcade games. Depending on the game, the price of a working arcade cabinet can be quite reasonable or very expensive. Games which were wildly popular in their day, (for example, Street Fighter II), will be easier to find than games few people have heard of. The price ranges vary greatly, but expect to pay anywhere between $500 to $3000 to nab a classic arcade cabinet in good working order.
Another alternative is to buy or build an arcade cabinet, and retrofit it with a PC running MAME. This can get tricky unless you're a whiz with electronics, but it allows you to have a good looking arcade cabinet which can run any of the games available for emulation. This is a popular choice for arcade game collectors, and you can find many online sources willing to sell empty cabinets or even fully configured multi-game systems.
Sources:
http://en.wikipedia.org/wiki/Arcade_games
http://en.wikipedia.org/wiki/MAME
http://en.wikipedia.org/wiki/Arcade_cabinet
http://www.videotopia.com/games.htm
http://www.arcade-history.com
http://money.cnn.com/2005/05/10/commentary/game_over/column_gaming/index.htm
http://www.gamespot.com/gamespot/features/video/dk_history/
http://wiki.media-culture.org.au/index.php/Computer_Games_-_Violence_-_Case_Study:_Mortal_Kombat_and_Manhunt