Hmmm... being the self-proclaimed Lord of the Pin Trading Weekend Spectacular, I do have problems with folks saying that there are only certain pins they accept.
In the past, I have been able to trade ANY pin I can buy. Usually I pick a signature pin and load up on it (like the Disney's California Adventure pin which sells for 50 credits in the Emporium) for events such as these.
Now, with my schedule and no Pin Trading Weekend in the recent past, I haven't pin traded in a while, so my information may be a bit out of date. But I DO remember talk about Hosts only accepting 500 credit pins last August/September, but I was still able to trade a 50 credit pin.
It's not like the Host is going to boot you if you aren't willing to trade a 500 credit pin-- if you're feeling gutsy, give the 50 credit pins a shot.