traveling on business.  If your work takes you to AZ and MN in the same month, and you intend to see providers in both cities, comparing rates would be prudent.  Most mongers seeing a reasonable number of providers have good insight into what you get at what price points in your local market, but as GaG points out, there are a lot of ways to overpay when you are traveling if you don't research your destination market before you go.  

"I would think AZ rates would be higher due to many unique factors (rarity of providers, outcall expenses, etc.). "
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Actually, when I was making frequent business trips between LA and PHX, the AZ talent tended to be 25% less than the LA market. There are plenty of local women who are poor/unskilled/bored/college students/retail-minimum wage workers in town to fill out the ranks of available providers.  
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My (unscientific) theory; local rates generally are based on some multiple of cost of living - more specifically average housing costs.  If a typical one room apartment rents in PHX for say, $800 a month, I would expect to see local rates at 20% to 40% of that, or $150 to $300.  So figure average rates for an "average" apartment in-call could be estimated as Rent x .3 = average rate.  
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Its a fairly practical formula. As it means a hooker needs to book 3-4 clients a month to pay  the rent. All other bookings pay for other stuff...  
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The higher the real estate market, the higher the rent (or mortgage), but the lower the multiple. So in NY, where rent in Manhattan could be $2,000 to $3,000 a month, I expect rates to be $2,500 x .2 = $625, give or take about 20% (range $500 - $750).  
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Like I say, not scientific, but it's been a fairly reliable method for me when travelling in the US.  Obviously, this is just a general guide. There are all kinds of exceptions (porn stars, high-end providers who cater to rich/elite, specialty providers, etc. vs. street walker, budget hotel hookers, BPage listings, AMP's.).  
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The double check to this math comes from simply looking at local ads in the main US sites. Not all have rates posted but enough do to form a general idea.
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Life is good
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The Cat

Indeed, and the rates have shot up big time over the past several years.  There are some great mature providers there whose rates have stayed steady but for the gals under 35, or so, it’s been a whole different ball game.  I imagine it’s this way in a lot of markets, if not most, but it just seems like Vegas has gotten crazy expensive.  Yep, lots of guys with lots of cash.  Kudos to the providers bringing home $1200/hr.