How about a 90 mm or 102 mm Mak? The OTA is only about 300 mm long, so will fit into a suitcase or backpack easily. Add a compact but sturdy tripod and a couple of eyepieces, and you're good to go.
My 90 mm Mak
http://julianh72.blogspot.com.au/201...0-mm-f133.html only cost me about AU$250 (including delivery), and it came with a 45 degree erect image diagonal, so you can use it as a terrestrial spotting scope as well as for astronomical use. I also bought a T-Thread adapter to fit the rear port, so it can also do duty as a 1,200 mm telephoto lens for my DSLR.