In some cases, there isnt much of a difference. There was a long thread on here a while back where someone broke down the whole thing. It turns out that if you really want to, you can buy different sizes of fishing line and use them as uke strings....and it's SUPER cheap. I dont know where the thread is at this point, but I would suggest doing a search for it if you are interested. It was quite interesting and he layed out the cost as well as the test size of line needed for GCEA. I've never tried it, but I would be interested to hear how it works.
Hope this helps