1. 12V AC-to-DC regulator. I think I found your $9.99 regulator, but how about $8.99 for a 2-pack?
2. Wireless relay. Could not find the 2-channel module you show; I wanted to confirm 12V operation (some of them operate on different voltages), and see what's up with the 3-button remote(?). How about $10.99 ($12.99 less $2 coupon) for a 12V relay module? Many of these listings say batteries not required (and hence not included). But this refers to the receiver not requiring a battery. In my experience, if the fob is included, the battery comes with. But I suppose it's worth confirming. The fob appears to be the same one I used in which case it's the inexpensive 12V A23-style battery.
3. DCS 22uH inductor. You do not need a military-grade component - LOL . How about $5.79 for 25. It pains me to suggest this for what should be a 5 cent part but here's the math: Regulator $8.99 + Relays $10.99 w/coupon + Inductor $5.79 = $25.77. Ta da! Free shipping from Amazon with $25 purchase.
If you are using 18V AC track voltage to supply 12V DC, install the inductor from the 18V AC "hot" to either one of the inputs on the regulator module. The 18V AC common goes directly to the other regulator module input. And, to your point, yes the regulator module "drags down" the high-frequency DCS signal; the inductor demotes this loading while allowing the low-frequency 60 Hz power to pass through.
And point well taken about getting stuff more quickly. It might be half the cost if willing to wait for eBay Asia but would be dealing with multiple sellers, un-tracked packages, etc.. I don't know if this is nationwide but I get a message saying my Amazon package is about to be delivered with a live GPS map with a dot showing the delivery truck... it's amazing how the GPS image is real-time so I can watch the dot move and walk to the front door just in time to see the truck pulling up. Or else a few minutes after delivery, they send a photo of the package sitting at my front door. Full disclosure, I do NOT own Amazon stock!