So, I mentioned in my half-assed attempt at a half-assed anniversary post that I had made my own set of rules and a supplement for the same. I'll be quoting the optional rules for building your own starfighter-class ship from scratch below.
If the players or referee wish to design a custom starfighter, use the tables [below]. Primary attributes start at d4; each upgrade raises that attribute one “step.” Note that STR (weapon) upgrades can be taken more than once, so buying twin laser cannons twice gives you quad cannons. AGI and INT upgrades instead replace the lower-spec part. For calculating costs in game terms, multiply the listed Cost by 2,000 ₢.
I spent a few days tweaking the cost and balancing the various upgrades, to arrive at final totals for scratch-built ships that were playable while still being in the same galaxy as the actual listed cost for those ships (as detailed in official Star Wars RPG books, especially the d20 versions). The ones I already included in the supplement itself (with the serial numbers filed off) are as follows.