You need to get out of the mindset that price is a direct indicator of quality when it comes to scuba gear. Much of the price you see is about brand premiums and distribution models.
For example most of the retail price of Atomic and ScubaPro regs comes from the markup at the retail level and the brand premium they can charge in North America.
Zeagle and Mares and Hollis (and most other brands you find in shops) have the same distribution model costs, but can't charge as large of a brand premium. This also applies to ScubaPro in Europe.
Deep6 designs, manufactures (actually outsources the manufacturing to Taiwan, but that reduces costs at their size), and directly sells their own gear, This allows them to undercut the pricing of the other brands at any given quality level.
DGX is a big reseller. I don't believe they make anything, but they do contract for various products under their own name. They can sell these direct to the consumer at a very reasonable price.
Back to the regs. Deep6 is an excellent choice for your current and future diving conditions. Sealed diaphragm regs are inherently well suited for cold and murky conditions. The company was founded by Chris Richardson (
@cerich on the site) who had previously designed the regulators for HOG EDGE which are also good choices.
I'm also not a fan of sealed piston regs. Sealed diaphragm are actually sealed, there are 2 rubber diaphragms between the water and the working parts. OTOH, Atomic and ScubaPro piston regulators are sealed by packing grease in the ambient chamber which houses the main spring and the shaft of the piston. If it's not packed completely, you can get unseen corrosion inside the reg.
I recommend this thread for more on the differences:
Piston or diaphragm 1st stage ?