This sounds like it'll be a fun game!
for 10 euros, i think I'd want at least 10 levels, cause there probably won't be any storyline to play through, so there should be many levels. if you can make more than 10, that would make it even better, as long as you keep the quality up and make each level unique. i think for 5-10 bucks, 7 levels would be the minimum I'd want to see...
Keep it up!