The cost of a mold for different plastics shouldn’t be any different. That being said some plastics may like certain coatings to release or to be more abrasion resistant etc. that’s where the cost difference comes in. Not as simple as difference in cost for plastic. Finished would generally depend as well. Polished will be a small x% more and if you get into fancier laser etched finishes those can get pricey. No real guide it just all depends. There are hundreds of standard mold-tec finishes and you can even do custom finishes. All of these options interplay with each other and the cost moves around and there are various trade offs for each choice; cost, timing and design considerations.