The lowest cost UPS-like device I am aware of that I would have reasonable confidence in, with respect to both the likelihood that it would solve the problem and its suitability for use in a quality audio system, is the APC S10 or S10BLK
, manual here
. I've seen good reports on it or its larger brother, the S15, from some reviewers and other members here. Unfortunately, though, it costs $900 at Markertek.com (a well known and reputable dealer), although some less well known sellers apparently offer it in the area of $650. Note, btw, that its continuous output power rating is 700 watts, which may or may not be adequate if you were to include your power amp in what it is supplying.
The devices Alan mentioned, btw, while most likely being excellent solutions, cost multi-thousands of dollars.
A question, though: I would expect that the refrigerators are probably not on the same breaker as the outlets supplying the system. If that is the case, are the refrigerators on the same AC phase (breaker panel "leg") as the outlets which supply the system? If so, perhaps the electrician could just move the system outlets to the other phase, and that would solve the problem.
Or if they are already on different phases, what I would wonder is if the DAC is responding to something other than a drop in voltage, such as RFI/EMI that is generated when the refrigerators turn on. If so, and if that is being coupled to the DAC through the house wiring (as opposed to through the air, which seems unlikely but is a possibility I wouldn't totally rule out), an inexpensive conditioner or filter might be the solution.
Good luck, in any event. Regards,