On the weekend I purchased a 45 L topbox for my bike.
A SHAD SH-45 for $290. The 50 L version costs $500, too expensive for my taste.
I was looking at a Givi 52L box, but they are USD $300, plus USD $180 postage. On top of that you needing the mountplate for USD $90

Now all I need are:
- Centrestand
- panniers for the side
- Protector for the bottom of the bike.