It sounds a bit expensive to me too. I'm assuming that the Amiga doesn't have an accelerator, hard drive or tons of RAM. You should be able to find empty high density diskettes far cheaper than that. If you are hopeless you might at least try to buy the machine without the disks. You can find everything from the net
There are many threads about transferring ADFs from PC to Amiga on eab but I'm not sure if it is possible or easy with a plain A500. Also check if the machine has extra 512K ram in it. If finding an Amiga is hard, finding one of these alone is harder. Even if you won't expand the machine you need at least 1MB of ram. If it's an A500+, it has 1MB ram on board.
I'm not in Greece either but at least I'm a bit closer