First of all,
Read this, and rules on bumping.
Second of all, if you only describe the req from the shield, we don't know anything about it, and can't help you. My guess is, the shields was uninscribable and had good mods, and as such is worth a lot of money.
Also, I am not planning on trying to explain why uninscribable shields would be worth more than inscribable, because most people don't tend to understand this.