The Singer 401A is a great vintage machine. However, what exactly do you want one for? They're not for everyone.
I had several vintage sewing machines that I finally sold to another collector. Why? Because I realized I preferred using my modern Bernina for all of my sewing. I loved the vintage machines, but they were just collecting dust. (Actually, I still have a few I couldn't part with in the storage roomm but they are covered against the dust.....)
I would not purchase a 401A on eBay. If I wanted one, I would scout the thrift shops, Goodwill, and sewing machine dealerships in the area, scan the local "for sale" ads in the newspaper, go to garage sales that mention sewing machines or fabric, etc.
If you really want one and eBay is your best option, you have to make sure that the seller is truly familiar with how to properly package a sewing machine for the trip. Most people don't know how to pack them, and many machines arrive damaged. Sewing machines are heavy, too, so shipping usually costs quite a bit. Shipping costs are not refundable on a return, so you are out shipping costs both ways if you are not satisfied with the machine. Some sellers can't even tell if a machine is operable. There are a few sellers on eBay who specialize in sewing machines and really know what they are doing, but you do have to be careful from whom you buy.