Cash Coin 10, What Year/Dynasty?

Unfortunately, with sites like chinesecoins and zeno.ru, it can be hard to know where to start looking. Unless you have some idea, you're just randomly clicking links hoping to spot something that looks similar.

In this case, it's seal script (with it's distinctive "yuan" character shaped like a little running man), and Song Dynasty is always a good place to start looking for this script. So click on "Northern Song", then work your way down the list of emperors. Eventually, clicking on Emperor Zhe Zong will show your coin - it's from the first era of that emperor, and the first pic is a match: Yuan You Tong Bao. This era dates from 1086 to 1094.

No, none of the cash coins you've posted in the past week or two have been "rare" in the sense of hard to find or valuable; they're all priced in the $1 to $5 range, $10 at most perhaps for the ones in nicer condition.