If you are on a strict budget, then you are probably going to have to rely on resin cast pieces. However a single resin part is probably going to cost $20 all by itself.
By the way, you should also state what version of the DL-44 you are desire as it could help with the sourcing.
By the way part 2, you should also consider a little more detail in your thread title. People who might actually be able to help with DL-44 info might pass up this thread. It is a big board and sometimes if a title does not catch a person's interest, they will just skip over it. Can you image what these forums would look like if everyone with a question about something simply posted "Does anyone know..."
Doopydoos is a very popular source of resin-cast kits and parts.
They are not super-accurate, but the casts are (supposedly) usually quite good and I don't think that you will be able to get cheaper parts of any kind anywhere.
Doopydoo did cast not a real Mauser pistol but a replica from Denix, and that shows. There are a few threads about "accurizing" the Denix replica of metal, and those tips should apply to resin as well.
Another option is you could always grab the new blaster Disney put out, and paint it up and weather or modify it. It's not gonna be very accurate, but it's probably the cheapest option for you. And if you have not done a lot of weathering or modification work, cheap toys, nerf guns, etc are all wonderful ways to build your skills and save your cash when starting out on blaster builds.
BTW, Doopydoo, which I mentioned above, has the Greedo Killer variant.
I once scratch-built a Greedo Killer scope out of aluminium tubes, sheet metal and body filler. I used bottlecaps for all the knurled rings and acrylic for lenses.
Look here for a blueprint.
The scope rings are medium-height Weaver scope rings. It and the piece of scope rail were (or are) off-the-shelf items used by hunters everywhere so they should not be too difficult to source.
Here is an old blueprint I made of the scope bracket. It could be made from sheet metal, bar and L-bracket with simple hand-tools. I am not too sure about the accuracy though. Some insights may have been made by other people on the forum after I made this. Do read the older threads about the blaster!
That leaves the front grille and flash hider. The grille would be better made of plastic: Sandwich together with plastic cement before sanding fins level. (I tried that with aluminium, and it was not that easy).
Look also in other build threads for scratch-built flash hiders. Lots of people have been creative with funnels and other found parts.
I have been searching for a Diagram of the DL 44 Scope Mount for a while now. I just found your Greedo Killer version (Great Job by the way) and I was wondering if you have ever seen (or ever done) one for the other version of the DL-44??