More expensive than the balloon, but not outrageous. The amount of gas needed is a function of payload size and ascent rate but 3400l would carry a 1kg payload to ~35km over about 2hr before bursting (based on a calculator I found).
It was tough to find pricing for helium, but one place had prices listed and would run about $350 for the gas. Assuming that’s normal pricing, one could hoist a little Lenin statue to high altitude for around $500 all in.