LEGO Imperial Probe Droid by SPARKART!, on Flickr,
and on LEGO Ideas!
Yeah, yeah, it's not super-accurate, but IMHO, it economically captures the look of the Star Wars Imperial Probe Droid. It's about 250 pieces, most of them commonly found. Check the parts lists and instructions on the LEGO Ideas page, maybe you can make one for yourself with your own LEGO collection.