There will be slight variation based on where you enter the Turnpike and how far up in Orlando you get off- but assuming you get on at I-595 the entrance just north of FLL) and get off in Orlando at the I-4 Xway ( a common place people exit in Orlando though there are other possibilities as well) your toll one way would be $14.70 if you pay cash and $11.70 if you use Sunpass ( which gives a slight discount for each toll). As far as I know you do not have to use Sunpass as the route you would take would always have cash lane option. You might want to double check on the Orlando Forum if there are any Sunpass only stretches there you would encounter ( I don't think so, but things are always changing). There are no stretches in the Ft. Lauderdale area that are Supass only as yet - in South Florida so far, they are only found in the stretch of Turnpike south of Miami on the way to the Keys.
If you do have a rental car and want to use a Sunpass for convenience , be careful which company you rent from- Dollar in particular charges a flat weekly rate($39 I think) - which is too high anyway and charges you that weeks rate even if you only use Sunpass on one or two days. Others like Alamo charge $2 /day plus the toll only on days you actually pass through a cashless lane. So, to go round trip to Orlando would only be 2days x$2=$4from Alamo or some other rental choices- a much better deal . I think that's small price to pay to avoid having to stop and look for change and party made up by the SunPass toll discounts. But be aware that the tolls are collected in small increments at a few toll booths en route up to Ft. Pierce( about 2 hrs from FLL where it then changes and you are given a ticket at that point and only pay the accumulated tolls all at once when you exit- so there will be no need for getting out change after Ft. Pierce. The Turnpike system is in a current state of change to an eventual all cashless system ( but not any time soon). Till then it is sort of an assortment of toll collection systems which is confusing enough for residents and almost impossible to explain to tourists.
The toll amounts I quoted will only vary by a dollar or two if you get on or off at different points in Ft. Lauderdale.
Edited: 12 February 2012, 9:22