Yeah, usertesting is available only for English speakers, but I do know a site that is for Spanish speakers, but it's rare to get work from there. The issue is @Zero that with $5 per 6 minutes audio, we might be paid $5 by 1 hour work, as transcribing is a highly time consuming work.
Try Upwork. You can choose different kinds of online jobs there depending on your skills. You can see the price along with the job offer.
