So you're in Portugal, and I get your needing to use Thomann. Anything you buy new will likely come with roundwound strings, so you would have to buy flatwound strings as part of the budget, if you choose to go that way.
I don't know what pricing looks like on items you would be interested in, but let me propose some general characteristics that may help you get an upright sound, but also give you flexibility for other contexts.
I'm also assuming that you will want frets - fretless is great, but if this is your main bass, and you don't have fretless experience, then that is not a great alternative for immediate satisfaction or jumping into alternative types of music.
* Rosewood fingerboard. Warmer, woodier tone than you'll get from maple or composite. At your price point, you won't be seeing ebony.
* Two pickups. This will greatly increase your range of tones. You may find that your best "fretless" tone is not necessarily the one that is the darkest or deepest. Upright has a pretty complicated tone signature, and just rolling off the treble, and favoring the neck pickup, is not likely the best answer.
* Which bass gives you the greatest tonal variety, based ONLY on how far you move your right hand from the neck to the bridge? This is really hard for you to evaluate if you don't have access to a music store, but a bass that is more responsive in this way will likely give you a better shot at producing an upright sound. You're best shot at emulating upright will not only come from your choice of bass, but how you pluck or stroke each note, and your bridge/neck placement as you do so.
All of that said, I'd lean toward a P/J design. Active or passive operation is not important, and at a fixed price point you may get better performance by passing on a preamp.
One last thought - over the decades, Yamaha has always impressed me as providing tremendous value and quality control at any price point.
And one very last thought - don't underestimate the extent to which your left hand can provide effects that make you sound more "upright." Digging in, vibrato, portamento - you have left-hand tools that will give you more upright-style expression.
Good luck to you - Tudo Bem!
what is a semi hollow bass tho?
