Other than Disney's ME, the only other free transit from MCO is going to be to airport-area hotels; WDW is too far away from the airport for that kind of service. You can always take the Mears shuttles, or even the Lynx bus system if time is not an issue.
Many of the hotels on US192 offer free transportation to WDW, but the service is usually not very good; the hours are very restricted, the buses are crowded, and they only drop off at the TTC, which means that you need to transfer and take another bus or the monorail to your park.
If you are offsite and CAN rent a car, I'd advise doing so; it makes the visit a LOT easier. Priceline works very well for rentals at MCO, and if you have more that two people in your party, will probably work out cheaper than a shuttle if you keep the car small.
If I had to stay offsite with no private vehicle, I would try to go with a DTD hotel; one of the ones on Hotel Plaza Blvd. They all run a decent bus service to the TTC, and the Hilton will give you access to EMH as well. If you don't mind a bit of walking, you can walk over to DTD proper and catch a bus to the resort nearest the park that you are headed to, then either walk to the park or transfer there for the park.
PS: Try to look at your TOTAL budget, not just your per-night hotel cost. Consider using Priceline for the hotel -IF- you are willing to also rent a car, because with Priceline you might get something with no transport options, and it could be a little bit further from the parks than you might have independently chosen. I suggest lurking around betterbidding.com to get an idea of what is possible. (And remember, Priceline does not ever refund money, so do your homework before you bid.)
Another option for you might be SkyAuction; they often have really good condo deals, which would allow you to cook your own meals and save some money that way.