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How do you find datacenters which will let you colocate hardware? How much hardware do you have? What was the cost?

I'm really interested in this kind of thing.

Can't answer the latter questions as I'm not OP, but you could start finding a colo here if you're looking at the cheaper end of things:

Also just googling "[major city name] colocation" will usually find results, though be warned pricing is often "call us" vs. stated upfront.