How much would you pay for an MP7 3D model?
For a low to mid quality model, without textures: $2; Same quality, with textures: $5-10; High quality, with high res textures, suitable for FPS? $10-25.
Keep in mind though, that this is just a estimate on this…
If you are going to build one, do try to do it to the best of your ability, one of the things the asset store is lacking is decent quality weapons.