The problem is almost certainly with your dive shop, not the regulator. Sorry!
Excellent mid-range regulators include the aqualung titan, SP MK11/(lots of 2nd stage options) and many others. For the kind of diving you described, almost any regulator that's in good working condition and adjusted well will perform just fine. What do you have now? Are you sure you don't just want to find someone who can fix it?
I have a good friend who had a similar problem, the local shop couldn't make his reg work so he bought a new one online, used it for a year, then didn't want to bother getting it serviced. (He would have had to send it back to the online store.) At that point I suggested he buy a used MK10/G250 for about $150, which he did, I rebuilt it for him, that was 3 years ago. I just checked it out, it's still working flawlessly. All it takes is: a regulator with a simple, proven design, someone with a bit of competence and patience, and a reasonable amount of care by the owner.