Check the Silverstone Sugo SG09 for a small case, as you can also fin an mATX in it, and with just 2 added fans on the case, you can crossfire.
I am also holding my purchase of an R9 280x in the hope for a non-reference R9 290 non-x.
So just hang in there, and keep on improving your build withing your budget.
Tbo, I would go for a little more powerful PSU, but that`s just me.