Welding Jar is effectively better for your artifacts at the price of not applicable to your creatures. I wouldn't think that the trade to protect spy is worth it; as you seem to be tapping out a lot anyway and playing for aggressive combo. I would personally run the Jar for the general purpose artifact protection, as well as synergizing with the combo being a 0 drop and enabling
Elusive Spellfist as a card in the deck, it seems to run multiple purposes for one slot which could bring you a lot more stability. You also have
Dispel and access to cards like
Spell Pierce for "protection" in the one drop slot against non-sorcery spells, or even
Apostle's Blessing.
Spell Pierce is relatively inexpensive after reprinting and I would easily consider the deck budget after that and
Welding Jar. If it's 20 bucks total, I would be surprised.