I started work on the tub for my book press earlier this week. The wood needed a lot of sanding. At first I tried this by hand using just sandpaper, then I remembered a quick tip that someone taught me as a kid. Staple the sandpaper to a piece of scrap wood. Not only does this give you something to grip while sanding, it'll also help avoid rounding the corners of the wood that you're sanding.
I took a quick look online to see how much sanding blocks cost. Seems like they run anywhere from $5 to $10. This one was made for a few pennies within about a minute, and worked great.