do you think it is cheaper to build Neutron Thrower or buy the matty version?
depends on where you go really and what you’re willing to do with it…
a kit containing most parts of the thrower will set you back about £90 or $150… then you need some tubing, acrylic parts, lighting and bits to finish it off… then patience with painting and everything else lol
Personally i’d always go for building parts over buying them… there’s something infinitely more satisfying about seeing something come together in your own hands and then being able to proudly carry the finished version, than just buying one from a store…
I agree totally! Do you know of a good tutorial video with part ideas?
most tutorials can be found on this site actually, there’s some great ones around for weathering, texturing, building, electronics…
I highly recommend the Nick-a-tron thrower set, it’s a great kit including metal pieces and grips, you just need some acrylic tubing and decals to finish it off… then add the electronics 
http://www.nickatronprops.co.uk/products-page/proton-pack-parts/gun-kit
Sounds like you’ve already been convinced to go the other rout, but here’s my input.
Personally, I went with the Matty thrower. You can buy two of these for about the amount you pay to build one functional thrower on your own, and that is what won me over. Is it a toy? Yes, but realistically, so is that very expensive pack you build to go with it. It looks good and functions for $150, plus you can still tap the electronic if you want to amp up the sound with a better speaker. Best of both worlds IMO.