Tirana+Durres itinerary

Hi, group of 4 friends, we plan on going couple days in Tirana and then for around a week in Durres.

As far as I know there are no trains, so only options would be a taxi or buses? How much should we expect to cost for a taxi from Tirana city center to Durres and then back from Durres to Tirana Airport? I've checked bus prices and I found fares from 3€, 6€ to 12€, why such a big difference?

Some comments in this subreddit also mentioned a direct bus from Durres to Tirana airport, which we would like to take on our return, are there also different fares for this one?

Besides Skanderbeg square and bunkers in Tirana, what else would you recommend to do? For Durres, are there activities, day trips you could do? I saw durres has ferry line going from it, what site is good for booking ferry trips?