We have an in-house artist full time, and create most of our own work, and have extensive clip-art collections. The truth for us is that it's often faster to create than to browse clip art. On the other hand, when a customer send a jpeg of a spartan they saw online, very ofter those images come from one of the big houses, like Shutterstock.com. I'll pre pay $50 and for that I get 5 vector images, when I feel like downloading them. Top quality too. However, I had Dave do a job for me I think last year when we were crammed, and I was happy with it, very reasonable, and the customer has placed 3 orders already...
Steve