i've been selling my natural-24-stat cats for ~15k each (a bit more if they have a matching personality stat that lets them excel at a particular job, and a bit less if they don't) - but blazer is a bit special in that their natural 24 is in strength and they have a natural 20 in agility as well (the two most desirable stats imo, especially for a fighter). they'd be able to hit legendary strength and excellent agility in villages with strength+agility mayor boosts, which is pretty huge for adventuring, so i'm valuing that combination much higher than a matching personality stat for a job and they're also fully-leveled as a fighter already, so you'd be able to drop them into your team and start wrecking stuff straight away!
with all of that taken into account, i think i'd be looking for 20k for them at the very least, but i'd be much more likely to take an offer closer to 25k! ^^