How long a sealant or wax will last is totally dependant upon how often the car is washed and/or maintained. If the car is typically washed 3-4 times per month then ANY sealant you apply to the car's paint will last 2-3 months before it needs to be reapplied. A good carnauba wax will give some protection atop the sealant but not much. The wax typically needs to be applied every 3-5 weeks to be effective as a protectant.
Jetseal 109 would be a good, fairly inexpensive sealant to use. I would even recommend a couple of coats be applied after the car's surface has been properly prepped ...... clayed at the very least. Jetseal will require some cure time between coats so plan to devote the better part of a weekend to the process. Any quality carnauba will work well to bring out the lustre of the paint ........ 50/50 Concours is also fairly inexpensive and works well with the Jetseal 109 product. Both can be had from Detailed Image .....