Depends on what the market will bear and your sales skills. There are installers who simply hand a piece of paper with a number on it and keep their fingers crossed. Others put a lot of effort into a quote and spend time discussing features and benefits to the potential customer. Quite often they will get the job since the customer is basing their decision on value, not price.
Pricing can be as simple as quoting a certain percentage margin (40%??) over the cost of goods. This would cover install fee and your profit. Others mark up the cost of goods and add an install fee based on the job. This quote may comprise of 20% margin with 20 hours labor @ $80 / hour. the labor would be based on new construction versus replacement (demo fee), trunk line routing obstacles, tower locations, keg stations, number of faucets, etc.
Concentrate on selling systems and upgrades that will assure your customers low pour cost and high resale. A great start would be to attend the
Dispense Institute @ Micro Matic.