Using an Apple Display Connector monitor with a MacBook Pro
Either get one from ebay as (Mike Scott suggested) or Google for a DVI to ADC adaptor. The looking I did suggests that the UK one may actually be the cheapest. 

The reason they are so expensive is that ADC carries the DVI connection, USB, and the monitor's power. (That's right: no separate power cord.) Any DVI to ADC adapter you get will, at a minimum, have to plug into your mini DisplayPort adapter and into the wall. Here's Apple's compatibility matrix, but their store links no longer work.

Good luck!