I just picked the weakest nomad on the steppe and spent a while playing and I don't understand how you can have this problem. First, gold is generated by your herds, but it's quite unimportant overall. You can turn herd into gold whenever you go hunting, domicile buildings generate it, you gain it on sieges in war as well as via raids, and you can get it by ransoming (but when you're still small, getting herd is always better). All those sources should be plenty. Second, herd income comes from domain fertility (modified by control) and from vassals and (more importantly) tributaries. Tributaries give different amounts depending on their contract obligations. When you force someone into tribute by war, their contract obligations start almost at the highest level, and you can immediately alter the terms.
At the very start of the game you might have a low herd income. If you're very small, just migrate immediately to a 100 fertility herder province. If you're larger and have several provinces, then raid and tributise your neighbours. If you have slightly less herd than your neighbours but a higher income, then just wait a little. Or raise your herd to horde conversion with court positions or by increasing your martial. Get a tiny power differential, and exploit it to quickly snowball.
And if you fail? Just migrate and try again. There's pretty much no way you can go wrong. Nomads are too easy.