I think just adding the two weapons' material components together should work.
Based on vanilla: $212,000 for parts, 2,200 Engineer Hours, 2 Alien Alloy
I thinking, and its too easy. This weapon its very OP.
The manufacture need Heavy Plasma and Blaster Launcher too. And i made 2 other new resources (for ammunition too). So the manufacture its chained.
This is now:
Heavy Plasma + Blaster Launcher = Heavy Plasma Blaster.v1
Heavy Plasma Blaster.v1 + Weapon Control System = Heavy Plasma Blaster.v2
1 Blaster Bomb = 2 Small Blaster Bomb.v1
1 Small Balster Bomb.v1 + Projectile Control System = 1 Small Blaster Bomb.v2
maybe some elerium and alloy