Yep. Diagonally mounted D400 (409-410) with steel muffler. This is a 5269G. I have one just like it. Mine's a 77 and had a chrome handle. I guess this to be about 1979. The 5269 is in my top 5 favorite LB's of all time.
I'd say it's worth that much. If there are no cracks in the deck, engine turns over and there isn't too much play in the crank, you'll be fine. Everything else can be fixed easily and cheaply. Having spark is a plus as well. Very nice lightweight mowers with plenty of power to do must jobs. Not the best carb or muffler used on a LB, but they work. I love mine.
Not from a collector's point of view, but as someone who uses his mowers for their intended purpose, it's one of my favorites. Reasons: it only weighs about 45 pounds, simple, great old D-series engine. Mine was "custom" built long ago with a D570 engine from a snow blower so it runs about 800rpms faster and has an extra bearing on the crank, but the D400 is mostly the same and still one of the best. The magnesium deck is lighter and stronger than aluminum and doesn't corrode as easily. It's just a great combination overall. I have an older model that's basically the same configuration (5239A) and it's awesome too. To each their own, I guess.