I agree with the suggestions to get another Janome, so you can share the bobbins at least.
Feet may or may not be interchangeable since the 6600 is high shank and most other Janomes are low shank. I bought a 3160 as my travel machine and it came with most of the same feet as my 6600 so that wasn't really an issue. (Although I think all the snap-on feet will interchange; just not any that get screwed on).
The 3160 is a more expensive machine than you're looking for but I hear marvelous things about Janome Jems and I think there's some of those in your range. Definitely check with your dealer and see if you can get a nice used one! A travel machine won't get as much wear so I feel a lot more comfortable with a used one, particularly if it's coming from a dealer.
Barring that; I've also owned a Brother CS6000i and it was a great little lightweight machine. Main drawback is it's REALLY light and would scootch away from me as I was sewing! Very sturdy though; my niece & nephew took it over on a visit so I sent it home with them; they're 9 & 13 and both play/sew with it often and every time I ask I'm told it's still sewing just fine! I think I paid about $150 for that one, on Amazon. It has speed control & needle up/down.