Old Singer & Jones hand-o-matics can generally be found for modest coin. Not much to go wrong, easy to get going, loads of help & advice locally & online.
Good starters but dont buy a treadle unless you have the room for it - it's a biggish lump when it's sitting in your house. Takes a bit of getting used to, too.
All-singing-all-dancing, cheap (£30 - £100) do lots but don't last two minutes; throwaways when they go wrong (the hardpoint saws of the sewing m/c world.) Avoid!
Simple, non-computerised domestics; straght, zigzag, coupla fancies, are generally good value. Often best inherited from wife, g/f, mum, granny who is upgrading or not using. Also generally god starters