Custom magic item creation standardization

Question

I run a rather lighthearted campaign that contains a number of re-flavored elements, including items. For the most part since these are based on published items their actual value for sake of crafting and selling is easy to discern, but items with no direct counterpart are a bit harder to calculate. Is there in existence a guide, official or unofficial to assigning value to homebrew items (which by that extension would help with craft time and the such)?

As a couple of examples of what I refer to- how would I actually derive the value of an artificer's +5 Use Magic Device item? Say I had a fighter type that wanted to get someone to craft an item that could produce a flaming scimitar effect at will (as a replacement weapon). Even something as simple as a magical spice that could reflavor anything to taste like a specific food (like a really weakened prestidigitation effect) would theoretically have greater impact that it first appears (especially in the hands of a poisoner).

I know that as the dm and it really is up to my discretion, but it would be nice to have some form of guideline to go by.

Answer 1

You can find specific values for all possible magic items here, as the SRD offers rules for pricing any spell or bonus into any magic item.

Be advised that this system can be abused pretty horribly (not that I'd ever have done that... nope) and that some of the magic items have silly prices when estimated by their concomitant spells

Answer 2

Brian's answer was exactly what I was looking for, but I wanted to add something I found for sake of completeness.

I found contained within an artificer guide a section giving pointers in pricing custom items. Especially found insightful was the summation near the end of the custom item section

And that’s how you know you’ve got a good price for any custom item. When you hit the point where you can say “maybe”, odds are that you either have the right price, or are very close to it. If its so cheap you immediately say yes, its underpriced. If you immediately say no, its overpriced. If it’s a maybe, then just like Goldie Locks, its just right.