It's a saving of about $180 (CAD), which is considerable.
However, for that you would need to:
1. Strip the model. AK do a paint stripper that's good for resin, as mentioned here: /how-to-strip-resin-models-t166.html
This stuff would also eat through any superglue that's been used, which could actually work in your favour.
2. Fix any damage. I can see that one of the weapons is bent, and the other has been snapped off. I'm not sure if there's any damage to the foot, hip or shoulder joins where the parts are separated, but it's something you would have to look at and possibly pin.
The intact weapon barrel could be straightened with hot water, but whether you could easily strengthen it or not I don't know. I've seen a video of Leakycheese putting a metal rod into a Knight lance, but I don't know if these are multi-part as standard.
The damaged weapon would definitely need pinning however, as the weight of it would make a conventional superglue or epoxy join next to impossible.
3. Replace the missing parts. This wouldn't necessarily be that easy, as you don't really get FW titan parts on bits sites!
I assume the missing plates are the ones on the thigh? You could possibly look to 3D printing, but you would likely have to find somebody to design them for you, which might not be cheap. Scratch building is also an option, but for something like this I wouldn't want to try it myself!
This isn't something that I would consider, personally. Too many unknowns, too much work involved. Given the effort required I would rather start from scratch myself with an official kit instead of relying on the quality of other people's work. It's more expensive, yes, but if I was spending £££ I would rather spend the extra £ and know that I'm getting something that's workable.