That analogy is kinda off since any car will get you to your destination. How well it will do that at night, in a thunderstorm, on a road subject to flooding at any minute is another matter. Would you want an old cheap yugo in that instance.
That does not mean you need to spend an arm and a leg. I want my back up pony reg, that I will be using only in an emergency if it is not part of the gas plan to be reliable, rugged, easy to service or get serviced, and capable of giving me all the air I need when I need it.
Over the years I have used Sherwood, Aqualung, Oceanic, and ScubaPro as that reg. Now I use HOG. But I also use them as deco and stage regs so they are the same as my back gas. If I didn't then right now for an emergency reg to use on a pony I would want something I am familiar with and trust.
If I were on a budget I have a couple options. First and because I sell them and it is what my GF dives is the Edge EXP. Retail 240 bucks with second stage and hose. Add a small spg and 6 inch hose (I don't like button gauges - too hard for these eyes to see) for around 75 bucks and you have all the reg you need. The EXP is a balanced diaphragm, with adjustable second stage and lightweight braided hose. It breathes as good as my HOG's
My next choice would be the Sherwood Brut. Around the same price but non adjustable second, and a piston vs diaphragm. Not that big a deal to some but I prefer diaphragm regs that I don't have to take the 1st stage apart to set the IP.
I would also consider an Oceanic Alpha 8 or comparable Aeris reg although the second is not adjustable for either.
These are the brands I have actually used and serviced.
And not because they are not good regs, they are, I would not consider ScubaPro or Aqualung simply because I have ethical issues with the way they treat dealers and end users.