So along that line of thinking, how about a pair of those dolly's you put under your wheels to push your car around. I know they have 4 casters on them and might be cheaper.
You could do that. Just remember though, that lifts the front end, which will exaggerate caster a little. In other words, it will appear you have more than you actually do.
As long as you make your adjustments so both sides are equal, you will be ok.
