Did a bit of research and found a few weapons that'd fit in very nicely.
Well, I like WWII-era guns, and I've noticed that the BAR and Morano Thompson fit into this category, so I thought, 'Why not?' and chose the Bergmann MP18.
(Short video demonstrating the MP18)
Has a fairly simple look with the magazine sticking out of the left side, guiding upward.
I believe this could go for 70-90k with a slower speed + 7-9 dmg.
I thought of a really sick shotgun to put in the 90-100k range, so I decided to go with somewhat of a newer gun with the Fostech Origin 12.
The Origin 12 is considered to be one of the fastest shotguns in the world. It has a gigantic magazine (there's actually two types of magazines for this gun, a slanted one like the AK-47 and a round one like the Morano Thompson).
The first magazine (shown @ 1: 34-1:48) shows a strong but slower gun. Was thinking that there could be a small amount of knockback added to it, along with 8-9 dmg.
Second magazine (shown @ 1:55-2:06) shows a faster version of the gun. I thought that it'd be cool to have a fast gun, however with a bit of a delay between shots.
I dunno, these were just ideas. Pretty excited to hear about the possibility of a new shop gun.