You could make your own marmite
You need some
flaked yeast - buy mine from one of those bulk food stores. Don't
use brewer's yeast or bread yeast, make sure it's the edible flaked
Then mix it to the required cosistency with soy sauce!
There are different soy sauces too - light, dark, mushroom soy etc. Try
each one and see which taste you like best. I prefer the mushroom soy -
it's closer to the real marmite flavour.
It's very satisfying, mixing the two together in a wee bowl, and you can make it as thick or as runny as you wish.
Give it a try - it's very cheap that way, and of course, there are no preservatives or caramelisers or other additives either.