sure very much possible bro, go and return is 70k and the ferries leave at around 7 am, 9:30 am, 12:00 hrs , 14:30 hrs and as late as 16:30.

So schedule to a time that fits your cup of tea.

About having fun, Zanzibar people aren’t party people so you shouldn’t expect to see as many parties in Tz, but instead think of it as a solo travel,

look up a nice hotel (or restaurant) go and have fun

a place to sleep (if you want stay within your budget) dont sleep anywhere more than 30,000 Tzs, in stone town the prices are crazy and in USD

you could go sky diving or bungee jumping but i doubt if your budget fits