One of the books has a list (Unwired I think) for makeing new parts YES it takes months to do EVEN years but then again your starting character is not a new born or even say mom/dad/ect ect bought/gave/made it for said new character.
as to case price it is an agreed on price as it is just the case it really can't cost that much. At most 250 nuyen.
I've looked, in every book I have, and the only table I find is on page 228 of SR4A and it specifically lists Processor, Sim Module and Wireless Radio, with a caveat in the text that the processor and wireless radio are upgrade modules:
You can also use it to build your own hardware upgrades; use the Building Hardware Table...
Please, if you can't provide at least a page number and book, don't state that something is RAW. Acknowledge that you're relying on memory and be prepared to be challenged on the claim.
If you can't find a price for your case, and you can't show where it says that "upgrade response + upgrade signal + case = commlink", you don't have much ground to claim that this is the methodology for building a commlink from scratch.
The only method I have found is to use the rules presented on page 138, "Using Technical Skills to Build and Repair", along with the explanation of the Hardware skill on page 127. Those two sections are perfectly clear that you need to have (or develop) schematics for your desired product, which means that you need to have plans for a final-product commlink (Erika Elite, for example) and base components as determined by the GM.