Kodiak nailed it up above - can I do what I do with a $300 Squier? Sure, sort of. From experience I know the constant maintenance involved will quickly make me regret the decision. I need always-on reliability. I need an instrument that I selected because it fit my body and playstyle, minimizing physical stress. I need something that has the specific sound for my playstyle, instead of the lowest common denominator P sound required by inexperienced sound techs.
I've been in the room with a pro who plays 20,000 - 40,000 seat shows fairly regularly. He will go on at the slightest provocation about how expensive instruments are dumb and all you need is a low-end P. Oh, also, he has 6 of them in a rolling case, and a bass tech who constantly restrings and maintains them between every show, and a small sound crew who are familiar with it, and a stage hand who is ready to do a fast swap whenever needed.
Yeah, that might have cost $400, but he's not living the $400 lifestyle.