If you want to grow quickly and are interested in this area then aquasition is the way to do it, there is nothing wrong in buying to grow you just need to cover yourself.
I am not sure on the price as I am not an expert. What I would do though is ask to take a look at the last 3 to 5 years accounts and your accountant would then be able to put a price on it.
Find out the essential running costs eg: how much is the P&EL, vehicle running costs, chemicals etc.
The most important thing is to make sure signed contracts are in place for each and every client.
When buying a company work on losing 30% of the current customers through the change but if the right contract is in place you will have the protection of the notice period on these.
Hope this has helped
Fox