Would they have had the budget and time needed to forge armor for Wun Wun before the battle began?

The showrunners or the Northmen? 

Again, I can’t emphasize enough: give him a weapon. A ranseur, a halberd, a trident, a partisan, a pike, a bill hook, a corsqeue (bat wing or otherwise), a fouchard, a military fork, a fouchard-fork, a naginata, a nagamaki, a fukara yari, a voulge, a scythe, a bardiche, a poleaxe, a lochaber axe, a bohemian earspoon, a bec de corbin, an ox tongue, a spetum, a glaive, a guisarme, a glaive-guisarme, a glaive-quisarme-glaive, a longspear, a lucern hammer, ANYTHING.