Get 10 packets of 8.5 X 14 printer paper. (8.5 X 11 works too, but not as well)
Make a tower for your keyboard. Make another tower for your mouse. Tilt your monitor back by putting something underneath it.
Adjust the height by adding or removing packets.
I have no idea why people don't do this immediately when they're considering a standing desk. Everything you need is in the printer room of your office!
Having said that, there are several reasons to throw a few dollars at the problem:
Tilting your monitor up is, itself, lousy ergonomics. My monitor is already balanced on a tower of books to get it to proper height when I'm sitting; another 18 inches and it will be like playing Jenga with my company's LCD.
Your first days as a standee will necessarily be the hardest. The feature where you can swap from seated to standing and back in five seconds with one hand will never be handier than in the first month. And if you skimp on this feature you'll be in danger of giving yourself a bad experience, needlessly.
I've since upgraded to boxes.