Okay... You can use Just about any Crankset you'd like.

That said (I tend to gravitate towards crank posts...) You have a few options... You can find a blowout deal on 9 speed 105 or Ultegra cranks and Bottom bracket, Go with another compatible unit, or you can go with one of the new Shiny 2 piece units.

I mention that because the new 2 piece setup has trickled all the way down to Tiagra 9spd, It's a VERY affordable crankset and dang nice for the price, and will be available in Compact or Double.

I have switched over to 2 piece for all of my bikes except my beaters, primarily for the ease of servicing and the stiffness compared to other cranks (I'm a hefty guy.)

That said, you shouldn't have a hard time finding a good deal on a crankset. since everyone is switching to 2 piece, often not even knowing WHY they are doing so you can get lots of deals on the older stuff... and it'll probably do you well for your project.