Moved from a crop sensor 7D to a full frame sensor 5D3 as main shooter last December, about $3800 for body, 24-105mm F/4L IS, spare battery and grip. If you can buy with this kit lens then you're ready to start shooting. Later get the 24-70mm F/2.8L II and you can sell the 24-105 for approximately $800 if you want to (i'm keeping mine so far as a good light general walkaround lens plus it has IS for steady video should I want to shoot some).
Extra costs for the change to FF include some monetary loss selling all my EF-S only lenses, having to buy "L" grade lens as some lower end FF lenses look good on crop where only the center portion of the lens is used whereas on FF you need good quality to near the lens corners due to the larger image sensor, more storage and processing time due to larger files (I shoot RAW), loss of telephoto effect from crop which means buying longer lenses to get image to fill frame as cropping a FF to get the same framing as on a crop sensor camera generally produces a lower quality picture than shooting the same scene on crop sensor camera with the same lens.
If you can deal with it (as i have had to do) then the results have been worth it to me (lots more in focus shots with the 5D3 vs 7D, better image quality with less noise due to larger pixel size, two card slots so can have a large slow SDHC as backup to fast CF so I don't have to stop shooting when the main card gets full, etc,).