I have 5 clutches of ball python eggs in 1 HovaBator right now. It's set up substrateless. It's been working beautifully for me all season. Cinnies are hatching right now.
Herpstat thermostat on it.
They are not small clutches. The average size is 8 eggs. So, I think you may be underestimating the capacity of a HovaBator.
(Now, if you used egg boxes in the thing, you could never do that...but HovaBators are really too short to put egg boxes in anyhow).
It does depend on what type of eggs you're fitting in there. '20 eggs' is a bit vague, we don't know if you mean corn snake or reticulated python.
If you find anything larger than a HovaBator that is actually inexpensive, let me know. I've been looking for years.
Animal Plastics has a new incubator that holds sixteen 12 quart tubs, but it is $799, which I would not consider inexpensive, personally. That doesn't include the thermostat, which would be another $100.
Assuming that's 16 clutches, I can fit that into 4 Hovabators for only $600 including the thermostats. All my eggs aren't in one basket (so to speak), and if one of them breaks (most likely literally, since they're styrofoam--the heat coil seems pretty bullet-proof), it's only 40 or 50 bucks to replace it.
Definitely consider all your options. From what I've seen, it's not truly worth it to move up to a larger incubator until you get into the REALLY big ones.
I wouldn't be suggesting it, except that I've tried several different solutions, and every year, the HovaBators with the herpstats hold the temperatures and humidity better than any of them, and give me perfect hatch rates. I finally decided, why mess with what works? Now that I've gone substrateless in them, I can fit crazy numbers of eggs in the things. I use two of them, and if clutches are laid close together, I just put one in each incubator, so I don't mix the hatchlings up when they come out. I write the female's names on the eggs, lol.
I'll probably need to buy another one next year. I have a Repti-Bator, I guess I might try nursing that thing along with some vermiculite, instead (useless thing doesn't hold humidity over 80% even with all the holes siliconed).
Go for it, if you're sure you want something different, but I recommend giving the ol' Hovabator an actual try before you make your final decision. Unless you're incubating reticulated python eggs.