shows us that you don't need money to have great bases.
Dollar Tree sells a pack of plastic palette knives.
I find palette knives useful when applying and contouring filler on bases.
I generally prefer metal palette knives, as I like the feel and they don't break.
However, the advantage of plastic is that you can file the width down to whatever you need. Above, you can see that I've made a custom palette knife for contouring filler between 15mm figures on a multi-figure base.
(You may say: but there is already a narrow-tip palette knife in the set! To which I reply, yes, but it's plastic, it easily breaks, and it is too pointed; the modified thicker knife is more durable.)