Well, mining is not very profitable if you stockpile all mined ore - with the aim to go for crafting later, for example. And if you start refining the ores before you have any source of income, it will burn through your credits in no time. Add exploring the systems/stations to that and you’re broke.
So if you’re going for a pure mining / refining carrier, you should sell what you get - at best possible price of course. While GBM is very easy to use and doesn’t require any additional investments, keep in mind that the prices are quite low (besides, maybe, for class 1-2 ores) - as it’s what other players are offering you and they want to buy it cheap of course.
Opening an own resources shop is the next logical step and it doesn’t cost that much. Then you can use emporium browser to check what price other players demand for their wares and try to compete. Class 3+ ores, refined ores and harvested resources will all sell for a higher price at an emporium than what GBM can offer. Meaning, aim for higher class equips (you get some from NPCs too) and train 1-2 refining skills to high level (at least 4). Grab free Personal Harvesters from missions and start converting class 1 ores to valuable crafting resources. As more and more players will start playing PT, they all will need those resources, tons of them - especially prices for derivatives will go up, I assume, as crafting consumes a lot.
When mining, always take Hydra mission for the additional reward - which can be significant for a rookie miner - and a faction standing boost. Try to do as many NPC missions as you can, even not directly connected to mining as long as you have the appropriate skills, as NPCs usually pay generously for your resources and sometimes reward you with unique pieces of equipment. Train one level of Dumont Freight skill and try to always take hauling mission when jumping between systems - the investment will pay of in couple of jumps.
You’ll see, in no time will the very existence of the docking charge be forgotten completely. And if you want to do more with your miner and don’t want to sell the resources, a second character for money-making would be a typical solution. My hauler is helping my miner/crafter set up all the production chains - return of investments is exactly zero so far, but that will change, oh it will