Paint and Body Finishing Materials

I'll preface this by saying I'm not a pro by any means...
Gas bubbles or need to sand excessively are issues with the body guy, not the product. Use the right product for the need. Otherwise it's all feel and muscle effort. Cheap materials will both be harder to work with, and you will need more to do it. That's a given because the reason they're cheaper is there not as much "stuff" in them. Primers shrink more, colors take more to get the right color finish... The lifespan is directly proportional to the work underneath and the storage environment. Again - not the product.
In terms of saving money... using an epoxy sealer to me is not needed. I like doing my work over bare metal, then using an etching high build over it. Then block, then sealer, then color, then clear if it's getting it. I also have used single stage acrylic enamel, blocked that out, and shot a higher end urethane clear over it with great results. You have to have a good supplier to work with to make sure what will work over what, but it can be done and last many years.