4 strokes are generally 100 bucks more than 2 strokes, I've had good luck with the 2 strokes, 49 & 66cc I tend to like the older carbs better they are simpler. 4 strokes can run all day in the FL heat but you will have to replace the crank with an extra wide one, most 4 stroke kits come with these. So the 4 will run all day but they are huge, pretty gutless with centrifical clutch and they are no quiter than the 2 strokes. (different but just as loud unless you build a modified super big muffler).The 2 strokes are much narrower and fit bike frames much better (& balanced). My 2 stroke mufflers are really pretty quiet and stock as opposed to getting an expansion chamber. I have plenty of power. My ride is a land yaught with baskets and all kinds of goodies. I can cruise at 30 but I like about 25 better, top end is 40 but to mutch vibration. I'm not a speed freak but I ride 5 miles each way to work no problems 10 or 12 each way is easily do-able but I wouldn't go more than 30 or 40 miles without letting it cool down good between rides.. You can get ebay or internet 2 strokes for $135 sometime shipping included. 4 strokes are about $299 for the kits. Whatever you decide use locktite on every bolt, and check everything often.. Good luck, have fun and be safe.
if you want a cheap 4stroke I saw a 4 cycle mitsubishi weedwhacker for under 100 bucks at Lowe's but you would have to build parts for the drive line and drill up some mouting plates from strap and sheet steel. Friction setups work good but the side mount style has really bad balance, even when riding a regular kit 4 stroke it seems like I have a watermelon between my legs, I like the bikes feel much better with 2 strokes.