Our 3D printing service typically charges based off the models volume, surface area, and bounding box. We don't factor in the grams of material as a variable. These measurements are put into a formula that spits out a price based on which process and material is select. This makes generating a quote very quick and easy for the most part. From Ankermake's website, they say the cost per gram of 3D printing can vary greatly depending on several factors, such as the type of 3D printer, the material used, the brand of material, and the supplier. On average, filament-based 3D printing materials like PLA cost between $0.02 and $0.10 per gram.

My recommendation is the one you know. If you learnt tinkerCAD at school, stay on that. If you don't know anything about modeling, start with a free one. Onshape and TinkerCAD are great options. If you are going to be doing this professionally, Solidwork or Fusion360 are fairly standard systems. The most important thing is to get good at what you know. You will be much farther and faster ahead then trying to learn some new software that you don't understand or have to relearn. Unless there is a good reason just stay with the simple on.

My expertise is in physical product manufacturing. That being said, I run a software development team and walk individuals through the process of creating a physical product with 3D printing. The process is fairly simple and here in this community the goal is to give you one on one access to me to develop your product efficiently and with a simpler format then is currently available.