Providing you have a laptop or a PC with decent specifications you will be able to mix and your songs with most DAWs coming with plug-ins and effects more than capable of giving you a professional sound. The big studio that i will be using as an example is abbey road studios, a world famous studio their online mixing costs £550 for 1-24 files and £750 for 25-49 files, these are both excluding VAT. Cubase (available on Windows and Macintosh) is less than £550 and will not limit you to number of files you are allowed. so why invest in having your song mixed at abbey road studios? The brand for a start, people are more likely to pay more attention to your track if it says it has been mixed at abbey road studios rather than “mixed in my bedroom”. The equipment used is a big factor too they will more than likely be using expensive possibly vintage hardware where as you may be limited to the stock software that comes with your DAW this hardware gives your track a completely different sound. This could be the difference between your mix sounding amateur or professional and that could have a direct link to number of sales.