I wish to say that I sell membership cheaply (in my opinion). Let's say for $99 for one year. What's the right way to say it on my site: 1.) Membership at only $99 OR 2.) Membership is only $99? One more thing... In this context "only" and "just" mean the same (interchangeable)? like "membership is just $99" or "membership at just $99".
At makes "only $99" something like a "place" or "point."
Meaning that you are subtly implying you have moved the price temporarily to $99, but it may not be $99 in the future. Or for some other reason the price may change and you are saying where the price is now.
You may want this subtle implication of price increase (though it can mean decrease as well) in an advertisement to goad the viewer/reader into a sense of urgency.
If the normal price of the membership is $99, then is is typically more appropriate.