Looking over the rules for attachments and mods for vehicles, I find it kind of strange that an attachment you would install on small systems (e.g. speeder bikes) would be the same size/cost/output as an attachment placed on much larger systems (e.g. Star Destroyer). Take the High-Output Ion Turbine, for example. The act of amping up the output of a cruiser's thrusters would require far heavier equipment than for a speeder.

So, here's how I'm thinking about houseruling the cost. The charts on page 271 give the base cost for the attachment of the smallest vehicle on which it can be attached. Each increase in silhouette beyond that size increases the price by 50%.

Example, a High-Output Ion Turbine can be attached to a speeder bike (silhouette 2) for the listed price of 5,300. But installing it on a silhouette 4 starship would be 11,925.

What do you think? Think the 50% increase is too much? Do you think it is too little? Can you think of a reason why the attachment would cost the same no matter what size of the vehicle would be?

I'd take the unmodified version as a bench mark for silhouette 4 (assuming they're written for the parties starting vehicle), and make modding smaller vehicles cheaper.

The reason I went with base cost being for the smallest possible vehicle is because there are a few that can't be installed on ships even as small as silhouette 4. Granted, this is mainly just the case with weapons, but it makes a consistent rule across the board and you won't end up with wonky comparative costs.