I used to do a lot of freelance work (videos) so I often needed images, AE templates, graphics, music etc. Got them all from Envato as they have the lot and I could use my earnings balance to pay for them which was handy. Depended on my workload and the needs of the project but was probably spending anything from $20 to $250 a month. Very rarely do client work these days so it's not that often I buy stock.