The wiki has a good page on JC which includes a chart that discusses the 'cost per combine.'
http://wiki.project1999.com/Jewelcraft
I think the best thing to do is to get your Int to 255 and then do the cheapest combines possible going up up up up and away. I have heard estimates of how much it costs to get your JC up to 200's + and heard it can be pretty expensive. Good luck though!
I got it to 170 without spending much and I didn't take anytime enchanting or selling my combines. If you're patient and spend a lot of time in EC selling enchanted combines you can cut down your costs.