Incubator build help

[BridgeportQuail]

1. Should I make the outside from a foam cooler or a plastic cooler?
2. Regular or cabinet incubator? I will be hatching 50 quail eggs.
3. If I do a cabinet incubator, how does lockdown work? Will I need to move the eggs to a different container for the last few days?
4. How accurate are homemade incubators?
5. How much did your incubator build cost you? I was aiming for $30 or under, is that realistic?

Thanks for your answers