There are lots of air compressor out there, but the ones we have routinely used are the oil less variety as they provide better quality air,
Below is attached information about some compressors we are familiar with.
The Silentair is from a US supplier. This is a highly portable compressor with an approximate cost of $600, we have routinely used this one for field operations where high noise level is not a problem and the portability is a must have.
The Parker is a compressor from that cost around $4500 and we recommend this for laboratory use where a compressed zero air line is not readily available.
The Ekom DK50 is one of the types of compressor we use at Owlstone and is available with a soundproofing cabinet.