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It's a numbers game, so I would contact several. Write a standard message, then copy and paste, and insert a little info from each SB's profile to personalize it. I would recommend contacting between 20 and 60 SBs who look appealing and appear to be in your price range. I would email about 10 per day starting about 5-10 days before tour trip.
I recommend NOT changing your location. Say you are visiting for work and expect to be back often. Say that you are looking for a pretty, sweet, interesting companion for dinner and some adult fun. By being a visitor, you will lose some SBs, but there will be plenty who are fine with your situation. It's better to be honest.
Right now, I can't think of any specific SBs I can recommend, but if you have questions about a few in D.C., feel free to PM me. I know about 6 guys who are active here and have a fair amount of intel.
You MAY be able to find someone for $300, but expect to pay $400, maybe $500. If you want an uber-hottie, you may need to go higher. It sounds as if you will already have a hotel room, so, unlike the locals, you don't need to add that as part of your SD cost.
Have fun!