We have gone through the process of joining an Affiliate network for a few of our customers in the past few years. I can give you some insight into what is likely to work, and not work....what costs you can expect.....and how to manage your expectations.
Firstly setup
Getting up and running with an Affiliate network, eg AWIN is not an easy task from a technical perspective. We recently integrated AWIN with a quite complex eCommerce website, and I kid you not the work took us around 40 hours to achieve the correct attribution of categories, discount codes and traffic source in order to assign the right discounts to the right affiliates. The sales people may tell you setup is "easy" and you will be up and running in 2 weeks..... but in particular for a network like AWIN, if you want to fully utilise their platform, the setup is complex, and requires significant coding work. AWIN have a plugin for Magento......they might as well not bother, as it is effectively useless.
The up-front cost, from memory was around £3k to join the network. there is then a monthly cost of a few hundred, plus a % fee on commission. Yes, the costs are not for the faint hearted.
Which Affiliate Network
You will not find a better one than AWIN. Full stop. You will find cheaper ones, with low joining fees.... but they will not have the membership or quality.
Conversion rate
The main thing to consider.....and I cannot stress this enough...... DO NOT jump into an affiliate network until your site has a fantastic conversion rate. The clients we have done this for have been converting on their website at between 10% and 15%. If you are not....or you dont yet know....then joining an affiliate network is the wrong thing to do. Why?..... because every time an advertisers drives traffic to your site, it has cost them 2 things;
1) Time
2) Money
No advertiser is going to waste either of these two valuable resources unless your site is converting the traffic at a fantastic rate. If your site has a low conversion rate, advertisers will quickly realise that the efforts on promoting your website are wasted, and will focus on better sites.
Commission
The other thing you need to be offering in order to drive decent traffic, is a good commission rate to your advertisers. Depending on your conversion rate, your advertiser needs to be sure that they are going to be well paid without needing to drive thousands of sales.
Some stats
To give you some real life stats of one of our better affiliate campaigns;
Network:Awin
Setup Cost: £2k (for technical implementation)
Joining fee: circa £3k
Monthly fee: £300
They are offering between 5% and 15% depending on product category. For this particular client it equates to around £3 per sale commission.....which compared very favourable against Adwords.
After 12 months the client has done around £12k per month of sales, and paying £1,200 p/m in commission. This is roughly half the cost per conversion they are paying on Adwords.
Summary
If your site converts VERY well......if you can offer a better commission rate than competitors on the same affiliate network...... if your products are prices competitively.....affiliate networking can be a fantastic revenue stream. It's not to be jumped into lightly, and its not a magic bullet.
The initial cost means that it is not a decision to take lightly, and you need to have a strong handle on your expectations, your margins, and your startup costs.
Best of luck.