You can buy the verizon mifi without contract, but the pricing of the plans don't change. You are still left with the insane paygo prices listed about, or the regular $30/$60 a month stuff.
I'm going to guess they will charge you to start & stop so you can't do that easily....
I weighed all the options and the ipad was the better deal for me. I keep my dataless smart phone to avoid the new "mandatory" $10 data crap, and obviously no new contract - because I'm out of contract and it's nice.
I'd like the mifi, but the pricing just didn't make sense in the end for my online needs. The ipad fills them, along with other needs so it was the best solution. Except, well, I sure could use it tonight! Lol!