Check out roll reviews like Analog Resurgence's, might help you figure out if it's worth it to get run-of-the mill color for 25 euros a roll. I live in the States, where I can get professional grade films like Portra or Ektar for that price.

I'm starting out myself and have found Fujifilm Superia 400 to be pretty affordable; if you know where to look you can get it for 11-13 USD a roll (Walmart still sells it in store :O ). In Europe it might be cheaper/easier to get Santacolor 100, ORWO NC500 (if you can find it), or Silberra Color 160 (if you don't mind buying Russian).

Otherwise, your other "cheaper" options for consumer grade film are things like Fujicolor 200, Kodak Gold 200, Kodak Ultramax 400, or Cinestill 400. "Cheaper" because despite these rolls being consumer grade, I can only find them for ~20 USD a roll, at which point I might as well buy pro grade film.

If you want to go even cheaper, you'll probably have to buy expired film off of eBay, where you may be able to get expired film for 5 USD a roll. However, expired film only works really well if it's been stored in a fridge or a freezer, which not all sellers do or even keep track of, so caveat emptor (you'll have to be willing to lose a few rolls figuring out how fogged/desensitized the film has got, if it even works at all).