I was in Petersburg last year with my friends. We have booked city sightseeing walking tour using https://petersburg.expert/tour/sightseeing-with-guide/ but we had to get to the hotel ourselves. There were a lot of taxies Moskovskiy vokzal in St Petersburg and Yandex taxi were there too. As for price, of course Yandex is cheapier but you negotiate for discount with private taxi drivers. Good luck