The B3 Deluxe theremin is a good theremin for that price range IMHO (I didn't try the Deluxe but I do have a plain B3, and have seen videos of people playing the Deluxe - check for videos of Thomas Grillo for example, and you'll see that it has a nice sound and it's possible to play very well with it). However, be careful, as it ships from the US. I don't know how customs are in Sweden, but when I bought my B3 Standard and got it shipped to Spain, customs made me pay a significant fee (sorry, I don't remember the exact amount... but maybe in the order of $30 or $50). And you may also need some money to buy a transformer, as the B3 (at least the Standard, you can ask about the Deluxe) operates on US voltage. A plain plug adapter won't do as the problem is not only the plug shape, but the voltage. I think my transformer cost something like $25 or so.
Additionally, if you don't have an amp around for another instrument that you play, you'll probably want to buy one. Although to get started, it's not strictly necessary if you have a PC with a soundcard with line-in output - you can connect the theremin to the line-in via a jack to minijack adapter, and you'll hear it through the PC speakers. If your budget is tight, that may be a solution until you get an amp, which will sound much better than average PC sound cards and speakers and therefore is desirable for serious playing.
It's also worth noting that another relatively inexpensive theremin has appeared in the market recently, the LV-3: http://www.lostvolts.com/ - I don't have one of these but they have gotten quite good reviews for their price, IIRC, and they have the advantage for us Europeans that they ship from the UK. This thread talks about them: http://www.thereminworld.com/Forums/T/28971/new-uk-designed-built-theremin-with-volume-loop-pitch-rod-etc
You can always watch some videos on Youtube to see if you prefer the sound of the B3 or of the LV-3. Thomas Grillo has videos playing both of them.