IP Transit Questions.

My company is relativity new to the IP transit world... we've been a "collocated" customer for some time; however the idea of buying IP transit is new to us. We're looking at the possibility getting ourselves on a fiber local loop (Onfiber), which heads over towards the Westin Building here in Seattle. My question is, and I realize pricing points will vary between folks... what could I expect to buy for IP transit once I'm in the Westin Building. For starters we're looking at anywhere from 10-20 Megs of IP transit. Thanks in advance... Rob