headlight bulbs are very frequently not the same for japanese, european, and american models. they can be, but just saying that frequently they are not.

that is a pretty big offset on the rims for a rwd vehicle. major bummer since it means neither of my sets of rims are going to fit. wa hoping to reuse at least one set for snows.

how much more do HID's generally cost

It's a little tough to put an exact number on it. A dealer will tell you they're worth OVER a $1000.

However, you can buy the EXACT Ballasts and Bulbs that OEM setups have Plus the A well made relay kit for probably under $400. The other Component is the Actual Optics (projector/Reflector). They range from $150 up to $500.

Or if you're talking Plug and play kits, you can get garbage ones on ebay for $40, or good ones for $150

although, If your car came with Halogens but HAD an HID option, and you want that EXACT setup, it's sometimes better to just pay the premium for it up front. Or else you save some money and do a custom retrofit, or a less desirable plug and play kit

The retrofit I did, after projectors, ballasts, bulbs, and a wiring kit from scratch came out to about $600. Worth every penny IMO.