I can't say I've really seen any in the Manchester area.
Somewhere like the Hilton on Deansgate might attract some as it's a bit more high end, but a lot of the hotels either have small bars that are quite often empty, or more like a Holiday Inn Express or Premier Inn type place where businessmen may be less likely to be staying if a company is paying. Could be wrong here though as sometimes a lot of workmen staying for local projects.
Usually seems to be a man, couple of men or families in the combined bar / dining areas whenever I stay locally. Most of the time it's cheaper to walk down the road to a local pub than pay £5.20 or whatever for a bottle of cider or something there.
The times I've been to Manchester Airport (Crowne Plaza, Holiday Inn Express etc.), groups and families all over the place so hard to tell if any working girls there.
The Radisson would be the most likely if there were any there. Seems to have a few business types / suits there that could be a target market.
Probably easier to go online / ring an agency to see if you could get someone to come to your hotel to be honest.
The bingo suggestion earlier might not be too far fetched if you can easily chat up women. There's one in the Wythenshawe area near the airport that could possible yield results.
A lot of council estate types in that area who might be after a few extra quid. They do stand outside smoking so could be approached then?
You could even be audacious and approach single mothers wandering around the shops in the same area.