I would set aside 8-12K for a R32 skyline. Some that you pick up for 8K will be that cheap for a reason. Loads of km's, bad panels and paint or absolutely thrashed motor etc. If you buy one for a lil higher it a neat clean car.
Then comes insurance of 1-1.8K for full comp if you go that way. And with the cheaper car something will need to be replaced soon enough cos its so cheap.
Don't bother getting a GTS, it is non turbo and too much of a mess around to turbo (via engine swap or bolt ons)
If it near 100,000km you will need to change the timing belt, maybe water pump etc. which can cost up to 1000$
If you don't have 10K get a S13 Silvia or a 180sx. They are cheaper and more common. But if u can hold out and save up get a R32 GTST, they are brilliant cars
/my 2c