RAM is not expensive, but that depends on where you live.
Since you only have 1GB of RAM, I am going to assume that you have a netbook and that 1GB stick of RAM is embedded into the motherboard which means you cannot replace it. It should have an available memory slot for you to add memory. You need to read the manual to find out what kind of RAM it takes. I recommend a 4GB stick of RAM if it is supported. In the US that generally costs between $30 - $40.
If that 1GB of RAM can be replaced, then I recommend 2 sticks of 2GB RAM for a total of 4GB which can be bought for roughly $30 - $40 in the US.