It's not rude at all to express certain requirements that are an important factor for you to consider leaving your current position which you are happy with. It's definitly in your interest to provide such information when contacted by a recruiter.
Being in a similar position (I'm quite content about my current role and my paycheck), I was also contacted last month by a recruiter (let's call her Mary) via E-mail and replied with (loosly translated via Noodle or what its called) :
First of all, I want to thank you very much for contacting me about this job offer!
For your information regarding any future job postings, I want to inform you
about the following:
I'm currently working as a senior lead-developer and project-manager,
with which I am extremely satisfied.
Should this change for any reason, of course, I'm happy about
new offers - but these should be at least € xxx.xxx gross per year for similar responsibilities.