Keep in mind a few things.
The actual Kubota bulletin PIB-2007-027 issued May 8th, 2007 states that Kubota (KTC) will be shipping a New Seat to dealers for every B and BX series tractor sold with the OLD seat, from May 1st, 2007 onward.
No installation compensation is being offered by Kubota, meaning, they are not reimbursing dealers for the 4 bolt labor to swap any of these seats.
I am going to "assume" that any B or BX tractor SOLD BEFORE May 1st, 2007 will have to purchase their new seat. Sounds like some dealers are simply passing the low wholesale Cost to the customers (like Messick's where they list it at $38) , while other dealers are applying a mark-up, as they do with most standard parts. They typically have a range for their mark-ups, a commercial account buying a lot of parts gets a lower mark-up (volume discount) versus us schmucks that walk up the counter once a year for a filter or new blades.
The $69 quote sounds like that dealer has applied his usual retail over-the-counter mark-up, the $49 price sounds like somewhat of mark-up, but not totally obscene, they are probably just trying to pick up their cost to order and inventory and sell the part.
Bottomline: Sounds like anyone who made their tractor purchase After May 1st 2007, gets a new seat, free, period. Otherwise, you should get one by ordering, and hopefully for a "fair" price.
If your dealer tries to Jack-you-up on the price, then simply order from a trustworthy, reliable and cost effective (Messick's for example) source.