I’ve been collecting 1st Ed Base Set for a few years now, and I think you’ll always be able to find Blastoise for a while yet. Compared to Charizard, it has quite a bit less demand. Charizard supply has been drying up a bit I think because not only is it one of the most wanted vintage Pokemon cards, but also because it has people from other hobbies collecting it more since 2020 due to hype/investors.
Anyway, 700 is plenty of pop to go around. Even if it seems ‘low’, they trade hands quite often.