You can sell a blood botkiller scattergun on Backpack.tf for 1.3 keys ( 1 key and 14-ish refined ).
Afterwards, it really depends on what you do with the money. You can buy a couple of neat-looking scatterguns if you want to replace your old one. In my opinion, a Factory New Plaid Potshotter Scattergun ( 3.44 ref ) looks really cool. Or you could just get a warpaint and a strange scattergun and slap them together if you want to still have a strange scattergun.
You could hold onto the key and hope that key price gets raised a bit, but from what I've seen the price has been around 40 refined for a key for a while now, so good luck with that if you decide to go that route.
You can also buy a pretty hefty pile of craft-hats and low-value hats with 1.3 keys, so if theres a low-value hat that you think would look cool on your guy, you can do that too.
Hope I could help.
EDIT: Ouch, I'm a month late. Sorry for the necro.