Most things that will get you better light will probably be $70+
The first thing that comes to my mind is a finnex fuge ray. Finnex makes great lights, and the fuge ray is their light that is for low light aquariums like yours, which means it's cheaper, and you won't have to worry about CO2
. It might be a good idea to read about PAR, it's a way of measuring light intensity that can be used by plants. I'm not an expert, but I think the fuge ray should give you better light than your existing light, but not so much that you'll have algae issues without CO2
, as long as you don't run it too long.
Here's the 30" fugeray, I think that's the length of a 20 long aquarium. If your tank is less than 30", then you can get a shorter light which will obviously be less expensive.
Also another thing I just thought of, make sure your java fern's roots are not burried because they need to be tied onto a rock or wood. And anazon swords are heavy root feeders so they need root tabs put under them in the substrate.