I have had hpv for 6 years. i know what to look for and know liquid nitrogen is best for me. lesions are small and rarely arise (1-2 times a year). why shouldn't i purchase my own cryogun and do treatment myself? it will save thousands of $$$ for me?

First make sure you really have persistent or recurrent genital warts. It is rare for them to continue for 6 years is rare, and there are other causes of superficial genital bumps. However, if confirmed and with a dermatologist's professional advice, maybe this would be OK. But it's not just cryogen cost: you would also need a supply of liquid nitrogen, which itself would be very expensive.