Perhaps if you already have tools, a work area, and decent skills you could do this. But speaking as a beginner who had a similar idea not long ago, I realized a workbench required a level of skill I would be unable to achieve without more practice and, well, a workbench. In fairness I do strictly hand tools, so it's it a bit harder and the bench must be much nicer.
If anyone is interested, I ended up just getting this apartment friendly bench for hand tool use. You do have to hold your foot on the leg when planing but it works great for the size/money.
You should grab three or four bags of playground sand to add weight to the base. For less than $20 you would not have to worry so much about movement while planing. For a little bit more you could get some dumbbells and not have to lose all the flat space under the bench.
If anyone is interested, I ended up just getting this apartment friendly bench for hand tool use. You do have to hold your foot on the leg when planing but it works great for the size/money.
http://www.leevalley.com/US/wood/page.aspx?p=66736&cat=1,416...