Which combinations count for this achievement?

Check here From the Wrath to the Risen [excluding the Vibrating Nucleus Gel]

Ah gosh. Those are pricey.. =P

N00b Picket Sign + Sun Marker = Not A Noob Picket Sign

I think this one is the cheapest, But not profitable.

Thats a Genetech combination.. not a legendary one(combining two legendary weapons)

For 5 combinations, 10 combinations etc do they need to be different combinations or can you do the same one over and over again?

You can do the same one over and over again.

Thanks for answering. That makes it a little bit easier then but it's still a long way off.

Acidtongue.. Riptide + Eternal.