A taxi from the airport to the center costs 35 to 50 Turkish Lira (YTL). For more information you can have a look at the website of the Antalya Airport Taxi organization.
You should not bargain about prices. Neither before the trip, nor after. Taxis are metered and the driver is supposed to switch the meter on. And pay the price on the display. Take only taxis from the official taxi rank at the airport. If you think that the driver has cheated, you can call someone from the hotel when you arrive there. But don't be paranoiac. The vast majority of the Turkish taxi drivers are honest. I have taken the taxi plenty of times in Turkey, and there has never been a problem.
Just note that Morocco is not a good benchmark at all. But you will see this later on.
Regarding your second question, I think that it is too vague. It depends on where you want to go. It is difficult to set a rule. In Antalya you have a panoply of possibilities: walk, taxi, bus, tram, dolmus. For trips nearby you may consider renting a car. Public transport will no ruin you. As an example, three rides on the AntRay tram cost 5 YTL and a bus ride costs less than 4 YTL.