A UPS will work nicely. Add up the total wattage of all heaters for your snakes, and get a UPS rated at least 3x that (or buy 2 smaller units and plug some heaters in one and some in the other.)
The really large expensive units allow adding extra batteries. Its the battery size that gives you the extended uptime when power goes out. Unfortunately, the home PC UPSs that are affordable do not have extra batteries available (ask anyway, maybe there are some now) so the only way to extend uptime is to buy a larger capacity UPS.
Example - You have 200 Watts of snake heater total. The UPS rating can be 400VA, but that small of a unit wouldn't give you much uptime when power went out. If they sold extra batteries, you'd be in business. So, you have to buy a larger UPS to get more uptime. That's why I say for 200 Watts, get a UPS rated at least 600-800 VA, and the bigger the better.