I've been thinking of getting a Samsung Tab A 7 or 8 inch here lately. Depending on options and size they run $120-$200. Factor in more for a few accessories and mounting hardware.
I'm kind of biased, I've had good luck with Samsung, they are mainstream, well known, and widely used. If you run into some issue you are a lot more likely to find info for your specific model. I have a Samsung S7 phone, and the identical operating systems between it and my tablet, running the same apps, is sweet. I buy an app once, install it on both phone and tablet. I use them as redundant backups frequently.
Android is Android, if it's running a version within the last few releases most if not all apps in the store will work fine. If you are looking at anything running older than version 8 or so you are probably going to get some junk you won't be happy with. Anything running a newer version of Android probably has all the hardware you'll need, I can't speak for other brands and models, but the Tab A line seems to do well at GPS and mapping apps.
I currently have a Tab A 10 inch, I got it hoping to use in the vehicle, and really it's just too large and doesn't fit anywhere on my dash and is too bulky for the dash mounts I have. It did the job well but it just didn't work out. I use the heck out of it at home though. It runs any and all apps I want just fine. I've had it set up as the moving map, pulling OBDII data from the engine for instrument overlays, and playing music through the Bluetooth to my trucks head unit all at once.
I don't have specific experience with Gaia, but I don't see why it wold be any different than any other app.
HUGE plus to the Android tablets is they allow you to plug in up to 128GB micro SD cards for expanded map storage. Most apps allow you to install them to the card so the internal space is not used up.