20L I would think a pair of Any you mentioned above would be good.
And I'm thinking in your part of the country you could get away with a pair for under 100$.
Not me though lol, I pay around 70-120 per frog but that's cuz i'm in canada.
I also have a water dragon enclosure that is 6ft high, x 4ft wide and 3ft deep.
Had it for about 2 years now.
WD's are lots of fun