Bottom line is that in your price range I don't think you can go wrong with either the B3 Deluxe, or the EWS. Here are a few pros and cons you may want to consider.
Etherwave Standard Pros: Can be acquired at a good price used as suggested in above posts.
Has a good range and acceptable linearity.
Can be upgraded at a later date if you decide to pursue your musical endeavor.
It's very portable and durable for transport if you want to do outside gigs.
Has a more "classic" theremin sound which can be modified to some degree.
Easier to resell if necessary.
Cons: I really can't think of any for a beginner.
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B3 Deluxe Pros: Good price point.
Easy to play and easy to follow Thomas Grillo with in his instructional CD.
Lightweight and portable.
Nice smooth string-like tone.
Cons: Weak sound for bass in the lower end.
Tone can't be modified (This may be a plus as it is less to fuss with while learning.)
It may leave you yearning for something better as your skill progresses.
I hope this helps and if you have any specific questions please post them here or contact me directly. I am also thinking of selling my B3 Pro and will let it go for a price you may like.
I do think another drawback is the lack of sensitivity in the volume antenna on the B3, at least on the one I have. At this point, I am planning to learn for at least a year on the B3, but I'm also interested ultimately in a subscope, whose sound I like very much. (Especially when Amethyste plays it.)
But I want to mention one other thing about the B3 -- when I first got mine, I thought the sound was really muddy and I was unhappy. As it turns out, there was something wrong with the wall wart, which ultimately got worse when a fuse in our house blew. I replaced it w/a different one (that also pushes 12 volts instead of 9) -- and the sound improved a lot. I'm not a techie and would never have figured it out without my husband -- I was ready to send the instrument back.
I think the whole point of this thread was to help someone make an informed choice about a first purchase. Now he knows what some people think are pros and cons to these options, and he's made a choice based on what he can afford, and has decided to accept its limitations. It won't help this forum stay alive if people then criticize his choice.