Flat-towing with all four wheels on the ground is the easiest and cheapest way to move the car around distances longer than can be traveled on the battery. Just make sure to leave the car in neutral and don’t travel in reverse!
Lots of tow-bar setups are avaliable for the RV market- including fancy auto-allignment features, even power braking systems. For this application a simpler setup is optimal. Given the Miata’s popularity with racers parts are avaliable off the shelf. Rennenmetal.com sells a nicely designed tow bar bracket that installs simply in place of the front tow hooks. It’s very sturdy and relatively inconspicuous.
Inexpensive tow-bars are available from Harbor Freight, Draw-Tite, Kurt, etc. for less than $200.
I put together a simple set up of safety chains from a towing chain from Harbor Freight, and set up a pair of Harbor Freight magnetic-base towing lights. They’re pretty chintzy but work ok.
Altogether the system cost less than $500 and is much quicker and easier to store than a trailer or car dolly, as well is easier to tow because there’s virtually no weight besides the car itself.