The Hamster pays $150 to 200 since he likes ladies with white teeth, that smell nice, and don't mind having sex on this thing called a bed.
The Hamster truly believes that all SW are on drugs and are willing to do anything for some money. There is also a safety issue - SW's are more likely to rip you off since their pimp has a quota (If SW Sally doesn't hit her quota, she gets a smack!)
With an escort you get a comfortable environment, a clean room, perhaps a shower, a girlfriend experience, and a modicum of safety. the girl might see one or two guys a day in a non-rushed environment.
A street walker gives you 15 minutes in a car, probably did 10 guys in the last 5 hours, smells of crack ( or the other way around!), constant danger of being busted by law enforcement, and your neighbors might drive by and see your car stopped at the side of the road (the privacy element).
Ditto all the above responses. Generally, an SP will give you a better experience for all the reasons listed above. Granted, paying more doesn't alway necessarily mean better service. But the safety, discretion and cleanliness are good reasons (assuming you find a good SP, there are some horror stories with SP too).
Perhaps during the peak cruizing years in the mid-late 90's may have given SP a run for their money (it was a cruizers paradise), but now with the street scene the way it is, SP are my choice now.