50% isn't really bad at all, but your temps are a little low. You'll want to try to get them up between 70-80 (mine tend to hover between 73-77 @ 45-50% humidity). It's supposed to be a good RH for flowering. Vegging my humidity was between 30-40%, now that I have more foliage my humidity has increased a bit in my grow space which good for me.

I would get a small dehumidifier (like 20-30pint) and maybe a space heater fan to blow some warm air over your plants from a slight distance.

but 50% humidity is not bad. In relation to your temperature though I would say not that great either.

If you're trying to cheap it out I would say that your plants will probably make it through just fine.