Most popular auctions with expiring domains are at godaddy, namejet, snapnames. Search for expired domains name its very easy if you have domains list. With a bit luck, you can drop good one with PR5 cheaper like $200, just need to know which domain have not fake pr. List of domains are not free, but updated dailly with aprox. 50.000 new expiring domain names.
When searching from keyword DHG will take your list of keywords and search each one, the pages will then be crawled to find unique domains to check availability of. The process is relatively simple but very time consuming when done manually or semi automated as was necessary in the past. Luckily now the job can be set and left to work while you do something else.