It used to be the case that record labels didn't expect to hear professional recording quality on demos.
The idea was that a great song shines through in the simplest presentation.
That's all changed. Present the best work you can!
Everything about your presentation counts.
Sure, it costs $$$, but the amount of time, effort, money spent can pay off. First you have to get in front of the correct people to be screened and make the cut. Follow the rules on the website of the company you are submitting your demos to.
However, if your song's words, lyrics, melody, flow, chorus, bridge, hook, style, genre, etc. fail to grab the screener's attention, it's curtains.
It's in your best interest to put your best foot forward by presenting a professionally mixed and mastered demo with the proper instrumentation. :)
Need help? Ask the forum. Need help personally, p.m. me.