David,
YIKES! 200 per minute x 60 x 24 hrs x 365= 105,120,000 annually? OK, you need the most expensive one ;) or buy the one from the USPS (documents at: http://ribbs.usps.gov/files/AMSAPI/AMSAPIUG.PDF). The usps provides many options and their prices are better than the comercial guys.

I have opted for batch processing and buy the blocks of transactions (100,000 for $500.00) - I know is not instant, but budgetarily it does the trick. They also provide a web service that can be easily integrated into .NET apps (name-searching.com)

-R!