Seriously, I don't use any expensive fillers in my work. The quality of the metal work under it is much more important. I've used cheap filler, even under Candy paint jobs, and have held up for 20+ years.
As for finishing filler/glazes, not much choice beyond Icing, and Evercoat glaze. To make it work a bit smoother, I buy a product called Smooth-Eze. it'san additional resin/thinner that makes the filler go on easier, and smoother. I use it a lot, as I dont' use filler much, so it tends to thicken up in the can, and this stuff restores it. If you dont' want to buy a bottle, I can send you an ounce or so to try.