Manually add values to items in collection

I would like the ability to manually add values to items in my collection for when the value on the price tracker is inaccurate, due to either eBay user issues or VGPC user issues. eBay user issues would for something like people continually listing PAL copies of Soccer Kid (which is worth almost nothing) under the NTSC Soccer Kid (which is much more valuable). An example of VGPC user issues are something like the Atari reprint of the NTSC Dragon Ball GT being used to price the original first print which is substantially more valuable. For cases like this, I'd like to just manually post a price for my item as a point of reference for when I check collection value.