if you're going to use money to advertise you have to focus your advertising on people who would be interested in this product.
for example it would be total waste of time to advertise to boomers on Facebook or to shit-libs on Mastodon.
on other hand there is quite a lot of transplants from GAB here on Nostr.
GAB is much bigger than Nostr right now so you could pick up quite a few people from there.
not every person on GAB is a nazi too. for example Dr. Robert Malone is currently under attack on GAB for not being a Nazi:
https://gab.com/RobertMaloneMD
he was smart enough to invent MRNA vaccine perhaps he's also smart enough to use Nostr if somebody got in touch with him.