Welcome back bro! We've missed your inputs, haha.
Interesting stuff about Jackrabbit. Are you referring to the BL1800? Quite difficult to find references to "jackrabbit" on the Rabbit website
I found the local distributor for Rabbit products in my area.. unfortunately they don't seem to give out a free sample
Cost wise.. BL1800 is around $50 I think.
Regarding steering, the differential method wont really work well for 4 or more wheels, unless it has threaded tracks (like tanks). Threaded or not, it'll still face lots of friction, which makes the motors work harder than necessary. As a compromise, we have two "rack and pinion" steering systems at both ends. We may not achieve neutral turns, but the turning radius should be good enough to serve our purposes! We do intend to have a motor for each turning wheel.. but we still need to decide on its positioning (keeping in mind about the turning axis of the wheel, whether or how many gears we'll use, using universal joints, etc).
Hopefully we don't need to worry about tracking the antenna if we are using omni directional ones. We'll see if the latter has a good enough gain.