So far I’ve found that pricing of metal to be much more confusing than wood and much less transparent.
I ended up paying ~$108 CAD (~79USD) for 3x 50" lengths of .120 304 stainless. That includes a 15% discount for ordering it online (for pickup).
However in my case the price varied dramatically depending on the lengths I selected. For example 3x 50" lengths (150" total) was around $20-30 cheaper than trying to order less steel by getting 1x 50" length and 2x 40" lengths (or something of that sort… I don’t remember the exact sizes I put in). So in my case they seemed to up the price based on the complexity of cuts (or penalize smaller lengths).
I also see that you only have 2x 12" lengths which I assume you intend for the Z axis. According to the parts list, the low rider needs 4 tubes for Z, just want to make sure you aren’t cutting yourself short.
Fun fact: I originally got super excited about the Lowrider because I already had 1" galvanized pipe sitting around from a past project and figured “hey that’s perfect!”. Turns out 1" galvanized pipe at the home center is 1" ID, not OD. Once again the world of pipe measurements eludes me.