You need the controller to test sew, it will not run with out it. The three pin plug is usually attached to both controller and mains plug.
If the machine is clean, oiled, everything shift and turns and you can provide stitch samples on two layers of cotton fabric it's easier to find a buyer. A complete machine with pedal and accessories will be more attractive. Prices vary a lot, there's not that much money in sewing machines anyway. This is one of the most sought after models and in nice condition and that's a pluss. Here they go for anything from the equivalent of $60 to $180. Selling price around $70 usually goes within a week or two. It can be a lot of work to clean up and get a 401a to zigzag and shift stitch patterns smoothly again, if you take on the job someone might be willing to pay for it. It original came with a brown or beige bakelite "button type" controller.