UMD lets non-magic users cast spells from scrolls, which is enough for the creation of a magic item. Since scrolls are easier to obtain than rare components, anyone with UMD should prefer it over trying to quest for materials.
It's good the components are worth money. That also means you already have some idea of what they're worth. Do you allow that worth to count towards the GP requirements for magic items?
I have in the past based on the rarity of the item. For example, some necromancer may pay 10GPs for the tongue of a ghoul, but upward of 100GPs for some vampire dust. The greater the risk associated with the component required the greater the cost. I have also worked that the mundane item in question (ring, shoes, cloak, ect) does not have to be of masterwork quality if the component used is of very rare type. The way I have played it is that the power of the magical component can out weigh the value of the material items and cost needed.
Here is an example, player want to create a lesser mask of giants with these requirements:
Craft Wondrous Item, giant form I; Cost 15,000 gp (lesser), 45,000 gp (greater)
You can go the normal way and use the 15,000 gold and spell needed or you can substitute the giant form with the heart of a troll and 15,000 gold to create the same lesser mask, but if while doing this you instead use the heart of a storm giant, I would say that as you go thru the process of creating the lesser mask, the fact the heart of a storm giant was used, the mask turn out to be a mask of giant, greater. This is to reflect that the heart of a storm giant is a much more potent item then the heart of a troll.
I just like to do this to add flavor and imagination into the game. Mind you that this does not mean it will always happen, but if the PCs role play well, then these things happen to them :-)