What are the costs

From an economic viewpoint, dedicated oil free dental air compressors are considerably more expensive than industrial air systems. For instance a dedicated dental air compressor suitable for two surgeries, prices start at $8,400 and go up from there. 

Whereas an oil lubricated industrial compressors usually retails between $700 to $1500 dependent on machine quality, and an additional $2,500 is required to add the necessary filtration set and moisture removal equipment. This is still more economic than an oil free system. It also has the advantage of being modular and the system is easy to maintain and upgrade, i.e. each component can be replaced as needed.

Usually dryer and filter sets have the capacity to deal with volumes up to seven surgeries, as $2500 purchases the smallest unit available for any brand and accompanying filter set. Usually it is only the compressor  that has to be upgraded if the surgery is upsized.

Another point worth commenting on is that in a modular style system, especially with reference to the compressor, if failure does occur, it is easy to connect another similar style compressor (from a hire company) knowing that the air quality will still be up to standard.

However oil free compressor and air treatment systems definitely do have their place. In colder climes and where the unit is to be housed inside air-conditioned air space and where room is at a premium, these compressors systems often are the best choice.