At the minimum resistance of 0.4Ω and maximum wattage of 30w... a single / dual coil RDA with an AFC adjustable for either build, I'd suggest 27 and 28 gauge for duals, and 24 gauge for single coils. If the latter (specific build) is a bit too hot (HF is a very warm 331 mWmm²), you can simply turn down the wattage.
As you're on a budget and will probably want clones, everything I refer to will be from FastTech in China. Prices will of course be higher in the US.
The single / dual AFC RDAs I'm referring to will have dedicated options, examples like the
Origen V2, with three sets of 3 holes, or a
Veritas, with a single large (adjustable cap orifice) hole aimed at a central coil placement, where either singles or duals can be fit.
Another, which I just started using myself, is the
Nomad, with a unique AFC where the air flows from a orifice in the center, positive post. Not a high flow atty, but one that offers very good flavor in either single or dual builds.
I'm sure others will come along with additional RDA choices.