Mining takes forever to level up... Jesus... Currently at LV 27. Goldsmith is at 32 right now, but damn is it getting expensive. It's becoming a grind to get the mats I need.
The best way to level mining is to do a
lot of field-leves. Unless they radically changed them, they are definitely the fastest way to get gathering exp. You can make some decent money while you are at it, too. You should be doing crafting leves to build up Goldsmithing as well.
Goldsmithing shouldn't be costing you too much money if you are a miner. Unlike Blacksmithing, just about everything that Goldsmithing requires can be mined. Building up the two will take some time, but shouldn't be too costly. I ended up much richer than the average player thanks to getting money from leves and making my own stuff when it was possible.
I can sympathize, however. It took me a lot of effort to level up mining and my crafting jobs. Just try to make stuff you can use, and don't waste effort on making a lot of stuff for no reason. Do be prepared to mine a lot of stuff though. I mined up about 500 pieces of mythril ore, and then burned that all up and more leveling up Blacksmithing, Armorsmithing, and Goldsmithing.