"Average" Advertising/Marketing Budget?

[Carl Ohai]

I'm studying for my agent exam, and I want to transition into a career in selling residential real estate.

I want to learn about how agents allocated their budgets for their real estate business.

I've talked with two different agents in my area, and they both gave the same answer in that they allocate between 500-800/month. They seem to treat their marketing costs they same way they treat their overhead costs (insurance, transportation, etc.). 

I've also read a few blog posts that indicate that you should assign something like 5% of your commissions to marketing. 

This seems.... foolish.... But I also don't know bupkiss about RE at this point.

What's the normal strategy for coming up with a marketing budget? In my mind, it would make sense to spend as much as you can (assuming you are actually getting a return on it) to fill your working ours with new business.