Anyone joined a network as an advertiser?

I'm not sure what product or service is that you're looking to place in networks but some things to think about in terms of expenses:

If you're offer is in the continuity niche, you may have to pre-pay for traffic depending on the network you approach...with the risk in the space networks may not be willing to extend credit so depending on how much volume you want, you may have to pay the network up front for the traffic...many networks wont require this but some of the larger ones might.

Call around to 10-20 networks and ask them what they "specialize in" in terms of method and niche...I'm assuming you have an idea of what kind of methods you're looking for, no sense in popping you're offer in a network that is 95% email traffic if you only want search you know?

Also when approaching networks ask if they have an in-house design team, i don't know how all networks operate or how many have in-house design teams but if they do have one, they are there for you, tweaking landing pages, creating banners, email creatives, ETC...you can save a nice amount of money using the network rather than out-sourcing your creative needs...Even if you're offer doesnt pick up steam in the network you just saved money by not paying for the creative work they do for you and your offer.

All the best.