Donovan Morningfire said:
Are you talking about a PC droid, or a new stock model droid?
If the later, there's no hard'n'fast rules for pricing beyond totalling up the price of droid gear/equipment. I did a quick summary of the R2, and from my numbers it should have a higher price tag based on components. Of course, that was during the first week of owning the book, so I may have goofed somewhere along the line with my math.
Rules for building a PC droid are explained in the Droids chapter of SECR, and can easily be extrapolated for non-PC droids. Again, they'll likely cost more than the stock models in the book.
I guess your calculations weren't wrong (without checking them myself). R2s are stock droids available on the free market. The player wants to build something from scratch, that will most likely be more expensive.
Going along the D&D lines, you would probably use these rules:
Make a Mechanics checks DC X. If you succeed, multiple the result with the DC. This is the worth in 1/10 credits you make per week. Repeat until you have enough credits equal to the price of the object. Pay 1/3 of the estimated price in advance for base materials. If you fail the check by 5 or more, you lose half the base materials and must start from the beginning
The question might be: What is X? I'd suggest something around 15-20. (The character should have the option to voluntarily increase the DC by 10 to effectively increase the speed of the construction)
That said, I wouldn't use these rules. It takes awfully long to build something with this rule.
Though you could still use them as a base.
My suggestion would be to modify the progress per week in some way. Consider these:
By expending more money to get standardized droid components, you can increase the progress per week by 5 or by 10. By paying 2/3 of the droids base price, you increase it by 5, and by paying full, you multiply it by 10. (This is only useful if you really want to build the droid from scratch, especially a customized one. Otherwise, you should just go out and by one from the market)