I've used both Airgas and Praxair locally. They were within 2% of each other price wise.
So far I've been paying $120-$130 for 30L. Friend pointed me to a place where I should be able to get it for about $2L, name escapes me at the moment, will update later. You can also check local welding supply shops, sometimes they have excellent prices
Hope that helps, prices should be pretty close seeing as you are nearby
