I already had a VIKA AMON table top ($19.99) with VIKA CURRY legs ($3.50/ea). With a set of CAPTIA brackets ($14.99 for the pair), and a LACK wall shelf ($19.99), it's possible to add a second level to your desk. Having the monitor and speakers up off the top gives you some extra room. Not a bad workstation for under 70 bucks.
The bracket mounts through the bottom of the desk with a large washer, which requires drilling a good size hole completely through the desk top. The upper shelf mounts using four screws in each bracket. It feels pretty sturdy.
VIKA AMON Table Top $19.99 - http://www.ikea.com/us/en/catalog/products/60117016
VIKA CURRY Legs $3.50/ea - http://www.ikea.com/us/en/catalog/products/50105293
LACK Wall Shelf $19.99 - http://www.ikea.com/us/en/catalog/products/10159099
CAPTIA Brackets $14.99 - http://www.ikea.com/us/en/catalog/products/40051196