In that case, in the interest of not screwing yourself, start with an i5 and NO GPU. Just run integrated graphics until you can afford a GPU. No swapping parts and losing money that way.
In the interim you can buy a previously enjoyed GTX 680 or something for peanuts off craigslist.
You could always look for a bundle in the for sale section of the forums and save yourself even more money. I am sure you could find a i5 2500k or i7 2600k, motherboard, and RAM on the cheap and then still have some money for a mid range GPU. Those i5/i7's are awesome CPU's for gaming and overclocking. Most of the time I purchase used now rather than new.