Hi Kixkur09, I've used this Doktor Kulit (Dermatologist) once to check an unusual mole and I thought she was pretty good. I found her details somewhere on the internet from other expats. Although, I can't really vouch for her English skills as we used Indonesian during the checkup. She told me that if I wanted to get a biopsy on the mole to check for cancer it'd cost about 2 million rupiah.
Apparently she's available at a few different places but this place is the cheapest.
Dr. Ariana Sp. KK
Spesialis Kulit & Kelamin
Quantum Diagnostic Centre
Jalan Raya Sesetan Nomor 20, Denpasar
Google Maps Link:
https://www.google.com.au/maps/place/PT.+Quantum+Sarana+Medik/@-8.679686,115.215118,19z/data=!4m2!3m1!1s0x2dd240e86f869ce5:0x3798e2d9b6cfb695
You have to sign up as a member before you can see her, but I think this only costs about 10 thousand rupiah.
Good Luck!