A thermometer that can record temps is ideal, but you can figure it out yourself with practically any thermometer by simply checking on it several times during the day and night. It will at least get you close to what your extremes are.
If you do decide to give nepenthes a try, and don't have much of a temperature drop at night, do try an inexpensive ventricosa / maxima hybrid first. Some can be exceptionally hardy and live in less-than-ideal conditions. My own temps during summer are pretty harsh for Nepenthes, 90+ during the hottest part of the day and ~75 at night. Winter is much easier, since a small space-heater is considerably less money and space than a "small" air-conditioner.
If you buy a Nepenthes before the onset of winter, you may find that it grows very well for you, only to have it decline and suffer once the warmer months roll around.