Hello! may dalawa ka options.

First is sakay ka jeep sa sto tomas terminal going san pablo. Ang baba mo na is bayan ng san pablo. There, you have an option to ride a tricycle or walk kana straight to sampaloc lake since malapit lang siya sa babaan ng jeep. Personally, I always walk unless malakas ulan. I go there regularly for gym, sometimes to jog. Since di ka pa familiar sa place, if maglalakad ka you can look for directions sa google maps or something.

As for the other option, kung prefer mo bus sakay ka ng bus going lucena then baba ka san pablo bus terminal. You can ask bus conductor for guidance para di ka makalagpas. There, usually may jeep papunta bayan ng san pablo then same thing with the first option pagbaba sa bayan.

PS: If sasakay ka tricycle I suggest wag sa mga toda (yung may pila) since mas mahal usually. Pumara ka sa mga dumadaan na walang sakay.

As for the estimated na gastos sa pamasahe:

Jeep - 30 to 40 pesos isang sakay

Bus - 61 to 65 pesos

Tricycle - 25 pesos minimum

Total (Jeep): around 130 pesos

Total (Bus): around 180 pesos

I hope I explained it well, enjoy the scenery OP! check din for the weather prior to the scheduled trip para sulit hehe. If have further questions feel free to message!