Hard to go wrong with the entry level Yamaha https://www.amazon.com/dp/B01LY8OUQW/ref=cm_sw_r_cp_api_glt_fabc_1Q8MPNQZP9X1GG0SMYZ0
I'm a total beginner and just got this to learn on. It's pretty cool.
You should get 88 keys ideally. Here's a few inexpensive ones in order of preference:
Have you looked at the Yamaha p71? It's right on the $500 mark on Amazon.
Contains 10 different tones, are you looking for more than that?
I randomly stumbled across this comment, so I can recommend one.
The biggest thing you need to understand about keyboards is that there are ones with weighted keys and ones with un-weighted keys. Weighted keys attempt to mimic the feeling of playing a piano, where there is some 'heft' to the key. This gives you more control over the sound and feel.
Unweighted keyboards are more like what would be used in electronic music.
If you want to learn piano for things like classical music, jazz, or disney tunes, you really want to use a weighted keyboard (unfortunately, these are also more expensive). You might be able to find one cheaper than this, but it's a great keyboard.
I've played piano my whole life for reference.