Price Checks?

[Bizarro]

I've tried, different areas of the internet but it was unsuccessful, just people asking how much or lowballing.

I can use e-bay and take the average price sold, but you guys know, that one day an item goes for 100$ the next day same item for 20$ so, it can make it a struggle.

Is there any section I could post and get opinions of people for the value of a fair trade?

Thanks for any info