I wouldn't do it without a car. We have done it many times with a car. Offsite shuttle buses are just too unreliable. I mean, they often only come once an hour, might be full, are shared among resorts. The only exception is maybe one of the high end resorts- but you mention saving money.
What you could eaily do is spend the first two nights at a Disney value resort, then tranfer to a moderate or deluxe resort. I've done that many times, and plan to do it again.
I'm guessing they won't let you on the buses with tons of luggage, and they do luggage transfers for free- but I did a resort transfer via bus with carry-on type luggage not so long ago. Maybe it was the exception, but nobody said anything to us. We didn't have lots of luggage, just like one carry on bag and one duffle.
Offsite you also have to think about getting picked up at the airport.A taxi will cost you enough that you could party cover a rental car.Somtimes you an get great retnal prices in MCO.
One more suggestion - and you'd have to double check with ME on how to do this- but the Hyatt AT the airport is quite nice. We have stayed there on the LAST night of our visit several times. It's nice being able to roll out of bed and be at the airport if you have a very early flight. The last time I did it though, we had a rental car (which was also nice because it knocked a day off our car rental costs) If you think you'll be really tired upon arrival, you coud maybe stay there the first night, (book in advance) and have ME give youa ride in the morning perhaps.