I've owned a dolly before, pulled 100s of cars from BCA Peterborough and BCA Bedford plus a few from here and there. Then I used to use taxis, £25 a time after a while I employed a driver, we both used to go and pick the cars up one at a time which was a bit time consuming, currently I am finding the most cost effective way is getting BCA to deliver them as it costs me £36 + vat a car from Peterborough (60 miles round trip), if I have 5 or more at a time (which I normally do).
With the driver it costs about £16 labour charge, £10 fuel in the car we go in, usually fuel in the car we bring back plus my time. (Which i can't put a price on). Per car
I have thought of buying a 3.5 ton gross recovery many times can't really justify it as either I will have to drive myself or get someone to drive it and that's more cost on top of running one.
With BCA delivering, I can spend all the time spent on picking up cars at the garage, which means I can see customers etc, and make sales.