As a person who has bought used speaker for over 30 years, it is a great option. But If you want new, you pay the price and then some lucky person gets to buy them used for a lot less. Like I said above listen before you buy whether used or not. When I mean buying used, it is usually from a local stereo shop where I get a full trade in value up to a year or two if I decide to upgrade. I don't have a problem with ebay/craigslist/thrift store/garage sale(buy a lot at thrifts and garage sales for cheap) if I can hear before I buy.
I didn't mention buying a receiver since all you will need with your sound card is an amp with passive speakers.
AHD880 said "will they sound significantly better with an amp/receiver for the same cost (inc. amp/receiver) as active ones in my budget?"
Great question, my answer, maybe. I know that doesn't help but most of the budget should be spent on speakers. They have to reproduce the sound. Inexpensive active speakers have to factor in the cost of amps built in plus the cost of speakers themselves.
The higher end active speakers would be great speakers on their own and have specific amps built for each driver, which in some ways is ideal. Problem is they cost a lot.
"I'm also thinking about the cost range and the overall sound quality, how does it increase with the money? I mean at what average price borderline will I hear a major difference in comparison with, for example, 200$ speakers? I can consider spending maximum ~440$ then if it worth spending."
Another great question, doubling the cost doesn't necessarily mean double the sound quality but a "rule of thumb" is spend 50-75%(the higher the better) on speakers so if you had a 440.00 budget, spend 350.00 on speakers and the rest on an amp.
Argh, I don't really like recommending speakers I haven't heard but I don't mind recommending certain manufactures and the links above for the PSB active speakers, you should be fine. If you doing sound recording and production, you may want to find a place to hear any speakers you might consider.
Happy listening, the Prisoner...