They are very nice guns and very few were made. Remember, the standard guns that sold for less than $500 are now commanding $1,000 for 12ga. guns and $1,500+ for the 20ga. guns.
If memory serves me, the sidelock guns were in the $2,000 range to begin with. What's the price?
Here's one at Cabella's: http://www.cabelas.com/gun-inventory---scarborough---browning---953702-bss12-sca.shtml