Do you have an old cardboard cutting board for cutting out sewing patterns on? Use that. Or use the spare bed.

I need to be able to pin knitted pieces on it.

You can get large pieces of styrofoam a a hardware store or get the foam mats used in children's playrooms, gyms and workshops from sporting goods stores or places like Target. The advantage of the latter is that the pieces fit together like a jigsaw and you can take them apart for storage. Put an old sheet over it and you can even mark lines with a permanent marker on the sheet for straighter blocking.

I use the back of the guestroom door, and office type push pins Just attach the sweater or whathaveyou to the back of the door with push pins...then spray lightly with water and leave till dry.

I recently purchased a blocking kit that I really like. It's made up of interlocking tiles, like you see at Home Depot for the garage floor, or those tiles that parents use for the floor of a toddler's room. Although I bought the kit, I think you could make the same thing by buying some of the interlocking tiles and covering it with a light piece of fabric. I like that the tiles allow me to create the shape that I need for a particular knitted item, and then breaks back down into 12" squares for easy storage.

Here is a link that might be useful: Blocking Kit