821/Florida Turnpike to 27. Do not worry about the toll cost as you will get a bill in the mail base on your TT's tag. Not sure why you want to see the lake as there is nothing to see. Big dike/canal around it with some places to get on top... Google maps shows a boat ramp at the South Bay CG (27 & Levee Rd) that would let you turn around and see the lake... mainly swamp looking area. A better choice would be at Pahokee where it looks more like a lake. If you put in LakeView Dr. Pahokee, Fla. and do a street view you can see what I mean. Pretty sure you will be disappointed that you went that far out of the way, but you will get to see a lot of Fla that will never be developed. I would take 441 N to Barlow's fish camp/SE 126 Blvd to get on 714 to I-95N to get to Sebastian.
Good Luck.