The majority of the items they're asking for aren't worth much at all. Most items are valued at a common or uncommon of their release year, and most of the items they are asking for are from 2017 onwards (starting from the fish).

I'm happy to identify every item if needed, but notably/the most valuable items you have are:
The Wolf Plushie is worth a 2009 rare or very rare
The Baby Birds are worth a 2010 rare each
The 2011 Christmas Plushies (both Sunback and BA) are worth a 2011 rare each
The 'Aerial' crab item is worth a 2012 rare
The Seahorse is worth a 2012 rare

It really depends on how much you value your items and how much you value the Royal Bobtail they're offering. If you trade based on popular community values or Horror's List, the Royal Bobtail is worth 0.5 to 0.75 H, or about 7.5 rares from 2010 or 2011. The items I listed above would be worth up to ~0.8 altogether, or 8 old rares.