I'm not looking to make a profit (but my electricity is flat rate so efficiency shouldn't matter).

I'm looking for a cheap USB ASIC miner (I'm in Europe so maybe €50 or so), that I can leave running connected to an old laptop or RPi as a hobby / out of interest. I don't mind what currency it mines. And yeah I know the boat is long gone in terms of making any kind of return on such a small investment.

What's a good one to pick up? Preferably as high hash rate as possible, but efficiency in terms of power consumption doesn't matter to me.

I see some on ebay for 40 - 50 euro or so, that have hashrates in the 100's of khash/sec, I get the feeling these are sellers trying to offload older ones. Any faster newer ones in a similar price range?