Ammeter Suggestions?

I am pretty sure that front bezel is the flange. Nice looking unit.

If you plan on running any higher current DC to AC inverter it may overload a 100a system.

Watching current shows you how much current you are using at that slice in time. If your battery is full, or 1/2 dead your 20a requirement will still draw 20a

voltage is a relationship to load. as the current requirements goes up, voltage goes down, PLUS the drop of voltage as the battery gets used up. if you want to know how much charge is left using voltage, you have to check voltage with 0 current.

But than your request was for inexpensive, so These may be out of the question.

Or Buy a battery monitor which tells you all about the goes into and the goes out of as well as amps and volts.

I bought one off fleabay that was digital LCD. It was about $10 and has worked great for years. I have both a volt meter and ammeter for both AC and DC.
I find it's good to have both kinds of meters. They both tell you different things and the ammeter is especially useful to find small, parasitic loads that a V meter wont reveal right away.

I bought a voltmeter instead of an ammeter. I wanted to know what is left. It was about $3.50 from Bangood in China.

Connected it up to my positive and negative, and it tells me to two decimal points how much battery capacity I have left. It uses a ton of power to run it though... I think about 1/10 of an amphour in a month.

It's just set in place behind the cover panel on the breaker box, I open the lid, and check out what's left. Very nice indeed to know if and when I really need to charge, and to know how much is being used daily.