The cost to fill a balloon with helium can vary depending on factors such as the size of the balloon, location, and whether you're filling it yourself or having it done professionally. On average, it may cost anywhere from $0.25 to $2.00 per balloon for a standard-sized balloon when filling it yourself from a helium tank purchased or rented from a party supply store or online retailer.
However, if you're having balloons filled professionally at a party store or similar establishment, the cost may be higher, typically ranging from $1 to $5 per balloon, again depending on factors like size and location.
It's advisable to check with local party supply stores or helium suppliers for current pricing in your area.