I called them and got more info. Here it is:
If the property has 4 units or less, it's free to post. Only get posted on apartments.com
If the property has 5 units or more, there are 4 plans
Diamond - most expensive
Platinum - 2nd most expensive
Gold - 3rd most expensive at $199/month
Silver - cheapest plan at $160/month
These are the prices after 20% discount that will end by August. Each one comes with 3 month contract. For example, the total cost of silver plan is $160*3. The higher the plan, the more visibility on their website; better ranking and stay on the top of the search results.
The listing is posted on apartments.com and other 4 websites: homes.com, apartmenthomeliving.com, forrent.com, apartmentfinder.com
I asked about the premium $349/mo. She said it's not a good deal because it's only for 30 days and the listing rank is even below silver plan.
I asked her whether the bulk of the traffic comes from apartments.com? She said yes. Hmm... now I'm tempting to do the free one. I used the free plan a few years ago and not impressed. Only 10% of prospects came from them. The other 90% came from Zillow.
Looking forward to hear from others who have used them. Thanks.
--99.128.xxx.xxx