I built two based on the plans by Ana White called Easy DIY Garage Workshop Workbench. I modified the dimensions to end up with a bench that was 24" wide x 72" long. Perfect size for bow building and other hand-tool woodworking.
I liked this design because no it uses cheap 2x4s, goes together with glue and screws (no complex joinery like some of the fancier benches), and the legs are doubled up 2x4s so it's pretty solid.
I would guess each of mine weigh about 50lbs ... so light enough to move around if you need but strong enough that if you add some weight to the bottom you can do some draw knife work without it dragging across the floor.
They're certainly not perfect, but I think I built 2 benches for $75 or something like that. 3/4" pine ply top, 1/2" for the shelf.
I always think about building a nice solid wood bench with a thick maybe 3-4" thick top, but then I realize my simple benches do everything I need. One day I'll add another layer of 3/4" ply onto them and that will add enough mass and stiffness to the top that I'll be happy for another 5 or 10 years.
Oh yeah ... for a vise I have an old 4" bench vise ... again, I always think about getting a new one, but this one works just fine. I may install a woodworking type vise on the side one day, but I'll keep my bench vise because it's just more convenient to have you're stave completely above the top of the table and not clamped onto the side.
