SQL Server Estimated I/O Cost in real units
The best numbers for IO you can get is to turn on statistics.

SET STATISTICS IO ON


and then run your query via management studio. The set option will work for your current connection, and the information will appear in the messages tab.

Then you'll get information on how many pages will be read based on your query.

Also for ease of parsing complex/large query statistics, I use this handy little webpage: http://www.statisticsparser.com/