It depends on how hard they are to earn, how common they are, and their stats. What kinds of items are you talking about? Because bentos, for example, are 500k'cs.
Iunno but personally I usually offer around 6c for a 500kcs item. 1mcs like 10 to 13c? Like kefo said, it all depends. Is the item is high demand? who's selling? rarity and difficulty of obtaining the item.... Generally I start out around the prices I listed above but it can still fluctuate. If you're buying just start asking if however much is enough, and if your selling ask for offers where possible. It's pimd, there are literally no set prices for anything.
I sell for original prices for what they always been sinse i started and sell ok. Prices on my alt wall