Bob P is correct that the Magical Express is free. Since you are staying at a Disney resort you certainly qualify. There has been some talk that Disney will eventually start charging for this service. But for now it's free.
I qualify because I am staying at a resort but because the reservation is in a cast members name there is no way to get the ME luggage tags to me. She needs to modify the reservation before I can get the tags.
Your $90 towncar price + tip....that was for a round trip, wasn't it? I had been thinking that Towncars are running about your $110-roundtrip/tip included price.
We used a town car a few years ago and it was awesome. I heard they will stop at the grocery store if you need them too. So that wouls be helpful if you need any items from there.
You are correct, roundtrip with an online booking discount or a coupon for about -$5.00.
Most will provide a grocery stop-check their sites for details though to be sure.