I agree, people should be able to respond with a price to a price check in trade chat. I personally use the trade chat logs to check for prices on items and only post a price check if I can't find any pricing. Having prices sent via PM only harms the community in general. Not only will there be more posts looking for price checks on the same items, but it will allow for "shady" people to scam others by saying the item is only worth a few copper and they will buy it off of them when it is really worth a lot more.
How about getting more moderators to enforce the non-trade related chat rules instead of punishing the rest of the community by not allowing the pricing information to be public knowledge?