A quick check of spreadsheet shows them as 1.5 keys.
It's not exactly a fully accurate source, but it's usually around about the right price for items.
So if you sell for anywhere around 1.5 keys then it should be fine :P
Honestly though, if people don't want to pay the 2 keys for your medi-gun, I say screw em and let them find someone else.
If that's the price you want to sell at then go for it.