Nestor is right. If you're new, it might take some time to build up a stock.
Hirelings, writs and refining will do this eventually. (And the quality of your return on all of these depends on your level, experience in that skill and/or points you've spent in passives in those lines. For example, don't refine raw materials until you're character has invested in the passives that increase your return.)
Prices vary between servers, but as a rough guide here's what I'm paying for tempers in guild stores (I make and sell a lot of armor)
Greens, all: 20-30 gold ea
Blues: ~50 cloth, ~100 wood and metal
Purple: ~200 cloth, ~400 wood, ~800 metal
Gold: don't buy a lot of these and always invest in bulk. Think they're currently 6k wood, 7k cloth, $10k metal
If you are a new player, the best option would be deconstructing green/blue & purple items for the improvement materials.
The next accessible way would be to refine the raw ore/wood/cloth/hide that you gather.
Refining should net you consistent improvement materials and is wise to put points into the 'Extraction' passive craft skills to maximize your return when refining raw materials.
Your return rate for refining is roughly;
15% green improvement material (or roughly 3 green mat for every 200 raw material you refine)
12.5% blue improvement material (or roughly 2-3 blue mat for every 200 raw material you refine)
10% purple improvement material (or roughly 2 purple mat for every 200 raw material you refine)
5% gold improvement material (or roughly 1 gold mat for every 200 raw material you refine)
Note: these drop rates are for crafters who have the extraction passive skill maxed. You will also see a small drop in these rates when refining lower quality raw materials like iron ore/jute etc.
The best return rate for gold mats is completing daily writs. Top level writs will drop gold mats 30% of the time.
Hirelings are an easy way to gather a few improvement mats. Unfortunately you will get only a small amount once a day.
Note: Clothing hirelings will always give you double quantities of material.
Average drop rates for improvement materials from hirelings are as follows;
Green ~10%
Blue ~40%
Purple ~30%
Gold ~2%
*Double these percentages for cloth hirelings.