I was milling about Hobby Lobby today and found something interesting and fairly inexpensive.  In their xmas stuff they've got clear plastic ornaments that basically are balls that split in half.  They're clear and look pretty nice and are fairly cheap too... I was thinking about scratch building an enterprise (yea right crazy thought), but It didn't seem like I'd find warp nacell fronts very easily, but there were a couple of sizes, of course you'd have to scale based on the hemispheres, but I thought I'd mention it here because you folks are fairly crafty and might find this info useful for other applications.  You'd need to saw off the hanging loops, but it looked doable.