All of the cheaper phones have that issue.
However, understand the difference between storage and RAM and how Linux (which is what Android is) handles RAM.
As long as you have enough free storage for the system and the running apps to store the things they need to store (they store things temporarily, changing constantly), the phone will work.
You have to have enough free RAM for the apps that are currently running (including the system itself). That means that in a phone with 512MB of RAM, trying to run a 1GB app is silly - there's no room to put it, no matter how much storage you have. But a phone with 387MB of RAM and a slow processor is going to lag - there's nothing you can do to change that.
However, don't look at the free RAM and decide that certain apps are "eating up all your RAM". Linux considers unused RAM to be wasted RAM, so it's almost always filled with something.
You want a lot of free storage, but you're not ever going to have a lot of free RAM. (You can use app-killer apps to free up a lot of RAM but that's silly. Android knows how to handle RAM better than you do, so let it do its thing and it'll run better.) Read
RAM: What it is, how it's used, and why you shouldn't care