These EM type of rares are really hard to say. They are really worth what people are willing to pay on it, and what you are willing to relinquish it at.
I can give you some past sale prices that I have seen, but keep in mind item value fluctuates by taking into consideration, the hue, desirability, how many are out there, and how often they can be found for sale...
1.Dirty Bear Rug (20)-unknown
2.Fragment Of The Rare Holy Net (10)-150m (around July 2012)
3.In Honor Of Takako, For One Year Of Dedicated Service To The EM Program (It will Spark when u double click it)(30) -150m and 200m I believe 1-2 months ago (might be worth more now--this is a really cool item imo)
The best way to find these prices is to put these items up for sale.
Best Regards,
Deca