I have a 1,500 (30' x 50') sf studio with 17' high ceilings (Quonset
hut, so only the peek is that high)

I've been leaning towards a propane tank outside and one of those
propane-powered shop heaters mounted up on an end wall. Are these the
best way to go? any other suggestions?

I've seen the Infrared heaters in home centers and costcos... are they
more efficient?

Cost is a factor for me.

1. As folks have suggested, a fan or fans as high up as you can get
them shall serve admirably. The object is not to blast the air, but
merely to bring the air at the top down to floor level to just kiss the
floor, so to speak.
2. Any insulation you can apply will yield a rather handsome return on
your investment.
3. Propane as a fuel is acceptable. The heater that you use must needs
be a vented one. Anything less is inapproriate for the task you
describe. If you want infrared, it will work to heat people & objects
in front of it as also heat the air like a blue flame heater. One is
not more efficient than the other; the former has 2 ways of heating
while the latter has 1 way of heating.
They shall both emit the same amount of Btu, if you compare any 2 that
are rated at the same heat output.
4. Unfortunately heating is no longer cheap. You may find ways to
reduce cost, (buying used equipment as opposed to new), but you should
now mentally accept that heating is an expensive part of living,
depending on where you are on the planet. Hope this helps.
Ashoke - heating.products.bz/lptype.html