You'll be lucky Karennina, I use Yavuz @ Tiny Akropol. This time of the year I would expect to pay about £25 per day for a decent car if the hire is only for 3 days. I had a jeep for 3 days last August and I think it cost about £22 per day.
You may get a banger for less. Our local supermarket was hiring a banger for £15 per day in May but it was a shed.