The Game Mastering Section (p 204) has a table with purchase DCs and the corresponding $ value. But there are gaps in that: e.g. PDC 15 equals $500, 16 is $650. If you want different values for DC 15 equipment, you have to vary that.
Also, financial rewards are expressed in wealth bonus increases, not fixed $ values.
On the d20 M website on wizards.com, there is an article about the Wealth system, where they have a formula to translate those increases into a firm value.
My best advice is to use the Charts from D&D or Star Wars d20, maybe multiply by a certain factor, and then use approximate values for the goods (by using the above-mentioned table: A Desert Eagle would be at around $1.200 for example, and ammo $ 40 per 50 bullets.)