Trust me - I know too well how it all adds up

but if you think about it: the quality of your water will directly affect your fish. The lights, substrate and other nice tank mates won't. If you are thinking of somehow upgrading, and your current filter isn't quite doing the job, cut out a few nights of going out (you'll be surprised how much you spend on a night out!) and save up for that filter. (I practically sit home all the time saving up for this, that and the other

no just kidding - I have a life).
It will be a very good investment - as long as you don't decide to upgrade your tank !
If you do introduce a new filter, just hook it up and keep it running alongside the existing filter for about two weeks. You can then remove the old filter and all should be fine.
But keep an eye on your nitrites and ammonia and make sure your tank doesn't go through a mini cycle.
I put off getting an external (due to the big outlay) for ages, but now that I have it, it's bliss
