My preference is a stainless steel dual-stage high-purity low-flow (gauged from vacuum to 30 psi, so delivery pressure range 0 psi to 15 psi) regulator equipped with a needle valve. Most specialty gas suppliers sell these. They maintain constant pressure at delivery nearly to the end of the cylinder, once set.
If you are cost-limited to a stockroom regulator for your cylinder, you might make do with a low flow rotameter equipped with needle valve. Omega has them in ranges as low as 1.1 SLM argon.
If you require better control than the rotameter, you're looking at buying a mass flow controller, but at that point you might as well have bought the regulator in the first place, from a cost standpoint. However, if you absolutely, positively must maintain (for example) 10 sccm +/- 0.2 sccm from the top to the bottom of the tank, then an MFC is the only way to fly. Get one a with a range just larger than twice your target flow rate, since they're typically calibrated for nitrogen or air and you'll need to correct for P10, and your sweet spot for flow control is in the middle of the range. Find one with on-board control and display, so no need to buy separate controller electronics.
I tend to over-specify gas pressure and flow equipment, probably a product of some of my early projects, but that's the approach that I would take.
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