I find all the specific "racing" shoes outrageously expensive for what they are, totally not worth it.
I would advice, depending on the taste for firm/soft sole:
For flexible sole: martial arts shoes (like http://***********/kr3gqn7). There is plenty of options for the sole material, from grippy rubber to hard plastic passing by string soles. 15 EUR or less easy.
For a bit stiffer sole: indoor soccer shoes, just go to the next sport shop and grab the cheapest. 20-25 EUR are easy to find.
Either shoe was designed to be used for running, jumping and kicking with precision and to be comfortable for hours of violent movements on your feet, which is much more stringent than pressing a pedal sitting in your living room.
I personally use a pair of indoor soccer shoes that turned out to be a bit too small for my feet (so I would get sore feet if I run a full match with them). But for driving they are fine, they are hardly bigger than the bare feet and have good grip. They will probably outlast every other piece of equipment I use for sim racing.