You have a few options but they are not good, depending on what your looking for. You could grab an old MPC kit off eBay. On its own its a crappy under detailed kit. There are some resin aftermarket upgrades for it to make it look better.
Revell has a small pocket sized snaptogether that is halfway decent, better detail than the larger MPC kit, but still small.
Bandai just released a smaller SD, at about 4 1/2 inches that has super detail. But again it's tiny.
Your next options are bigger, more detail and a lot more money.
The OOP Anigrand at 28 inches long is a great kit when you can find one for sale. They seem to pop up quite often though.
The last would be the 3 foot resin kit by Randy Cooper. The largest, most expensive SD is also the hardest to build based on what others have said.
If you want a good looking SD with out breaking the bank, have a look at the Armada gaming miniature SD. It pre built and painted, but is a decent size (about 9 inches) and can be repainted easily.
Hope this helps. All of the above can be found by Googling the names.