Alien Breed 3: Descent

Assault Rifle
- Rapid Fire Module - $4,500
- Reload Enhance Module - $3,500
- Damage Boost Module - $6,000

Shot Cannon
- Rapid Fire Module - $5,000
- Reload Enhance Module - $4,000
- Damage Boost Module - $7,000

Flamethrower
- Rapid Fire Module - $6,000
- Reload Enhance Module - $4,500
- Damage Boost Module - $8,000

Electro Link Gun
- Rapid Fire Module - $7,500
- Reload Enhance Module - $5,500
- Damage Boost Module - $10,000

Project X
- Rapid Fire Module - $7,500
- Reload Enhance Module - $5,500
- Damage Boost Module - $10,000

There are three weapon upgrades for each weapon as listed above. Buy any one of them for any weapon you wish, and the trophy will unlock.

I personally recommend getting the Damage Boost Module for the Assault Rifle first, followed by the Reload Enhance Module for the Shot Cannon. If you have credits to spare, the other upgrades are pretty much based on your playing style.