there are several places where you can top up. i normally buy my helium from NOX, we buy by the 'J' bottle or by the crate. the last time we bought cost $0.07/L. how many litre is your bottle? and what is max pressure? you'll know the total amout of helium for a fill. the one that we bought are medical grade, i think you don't need med grade for balloons, just industrial grade will do.... probably cheaper too.