The expansion seems a little over priced imo but I found this in the lotro FAQ:
Yes, you can purchase portions of the expansion separately with your Turbine Points in the LOTRO Store. These items will be released in the LOTRO Store on the same day as the expansion, September 5th. The prices are as follows:
Rohan Expansion Content: 4295 TP
Expansion Content includes the quests in the Rohan region.
Rohirrim Skinned Soldier on Landscape: 295 TP
6th Inventory Bag (Account-wide): 995 TP
Crystal of Remembrance: 995 TP
The Outriders Token: 495 TP
So if you are going to buy it, then it would probably work out cheaper to buy the low one and then use existing TP for the 6th bag and any of the other things you want
Oh and there is no instance cluster included with this expansion!!!