There is the example of LPG conversions, where you can take pretty much any naturally aspirated gasoline engine and convert it to LPG for a modest price.
So you can't remove the gearbox, or you'll have to place a new stand-alone differential, which will add significant costs.
I'm glossing over the details but you'd need about half a dozen precision machined features and like three or four parts that are specific to a particular ICE engine/transmission application. Dimensions are such that you could probably buy cheap axles for a common application and then have them machined down to make your part. Parts cost should wind up under $200ea unless you need something expensive to machine (like blind female splines).