I recently went through this with our Cross. I went for a Thule flush aero bar set up. I was all set to buy new but I did a search on ebay for the part numbers and found the entire set up being advertised for a Volvo V50 for £50. That may well have been a bargain but worth having a look.
There are the Thule parts that make up the kit.
- Thule WingBar Edge 86 cm roof bar one-pack aluminium | 721300
- Thule WingBar Edge 77 cm roof bar one-pack aluminium | 721200
- Thule Edge Raised Rail foot for vehicles four-pack black | 720400
Pros and cons with this set up. With it being flush it's narrower than some option but that is what I wanted as I didn't want the protrusion. You wouldn't want to take this on and off frequently either as it's a pain. Mine is staying on full time. No noticeable noise or mpg increase. Looks really neat. I'll try and pop a picture up later.