STOP what you're thinking about. You sound like you're new to the tool buying process.
1. A set of cordless tools like what you're looking to pick up will cost you in excess of $400 for something that's decent, and by decent, I mean is STILL going to frustrate you when you run out of juice in the middle of a cut.
2. If you're going to get a cordless set, don't bother with ANYTHING for your first set unless it's from Panasonic (and I don't think they have a circular saw) or the Milwaukee set that's Lithium-Ion (I believe, not sure of the type of battery at this moment). Those 2 will be the most powerful and/or longest lasting you'll find right now. The DeWalt set, while nice, is just as, if not more so, expensive than the Milwaukee set, and won't hold a charge as long.
3. Search around, or go online. You can buy corded saws with the blade on the left hand side if that's what you prefer. Are you left-handed? If not, it'll end up being easier to follow your line if the blade is on the right-hand side once you get used to it.
4. You haven't explained ANYTHING about what the phrase "doesn't really work out me to cut MDF". Unless that saw isn't plugged in, there's not a snowball's chance in hell that saw won't cut MDF. What do you mean about that? If it's a terrible cut, tell us if you're using the blade that came with the saw, or if you replaced it, and with what kind/type/teeth on it.
I'm guessing the blade on a $40 saw isn't going to give you the same quality of cut that a LOT nicer $15 blade that's designed to cut MDF will give when you put that on your saw.
First, you need to explain to us what you mean about the saw not working, and we can all go from there. You may be $15 away from an enjoyable experience with an inexpensive saw and a lot less headaches down the road.