What is your location? If in Asia there is a couple of good manufacturers who can build you what you need for much cheaper than the Dynacon’s/Odim/Lawson guys.
Fugro got a bunch of big systems built for thier FCV’s in Singapore.
If you contact Stuart Kendall at Cynergetix in Singapore skendall@cynergetix.com or tlilburn@cynergetix.com they could help you out.
Or as James said try Deepsearch they often have second hand units, Neptune Marine bought one from there last year that was pretty good.