I'd have a go at doing a broken-backed
seax, Dan.
If the blade is usable, great! If not, well at least you haven't wasted much beyond some time.
And, depending on how much metalwork you've done, you may have learned some useful lessons for your next attempt.
One's first few knives seldom look pretty, so it's worth trying something that won't cost an arm and a leg.
Actually, if this blade is cast, there are many inexpensive or free sources of medium-carbon steel (rotary lawn-mower blades, old vehicle leaf-springs or leaf-spring stock and some large circular saw blades and old files, to name a few). These can be annealed in a fire and made into very passable blades by cutting out a blank with a hacksaw or angle grinder, which can be ground or filed to shape. You can then send it away to be professionally heat-treated, or even try to do it yourself using a charcoal fire (I've done it in a barbecue, though it is a bit hit-and-miss under such rough-and-ready conditions). It is much more work than buying a ready-made blade or blank, but considerably cheaper, and very satisfying.