Hey Mungo Man. Welcome to the PC gaming community. Seeing your request to play triple A titles at a moderate price I scrapped together a couple builds for you. The main difference between them is the CPU socket, one I built around the new Skylake chipset, the other around the Devil's Canyon chipset.
Skylake -
http://pcpartpicker.com/p/F2prkL
> Notes: You can always forgo the SSD if you do not want the super fast read speeds. The GTX 970 could be swapped out for a GTX 960 and you would only experience a minor graphical performance hit. But this is the beauty of custom built PCs, you decide what you want and you can always upgrade down the path.
Devil's Canyon -
http://pcpartpicker.com/p/b3KcXL
> Notes: Same as the Skylake build.
Afterword: If you really want to crunch down on costs, then you can switch to AMD but I have not had so good experiences with AMD's CPUs and I haven't used one of their GPUs so I cannot give you a fair opinion that isn't biased.
As for upgrading this is what I started out with a year ago
http://pcpartpicker.com/p/bd447P
and this is what I have now
http://pcpartpicker.com/p/wMJthM
As you can see I added a second SSD for RAID 0, another GTX 980 for SLI, upgraded my RAM and motherboard, and added aftermarket fans for better cooling performance. After you spend some time with your rig, and you feel as if it isn't giving you enough, this is when you consider upgrading. Upgrades such as mine are not uncommon.
One more thing you will want to consider, peripherals.
This includes headset w/ or w/o a mic or speakers, keyboard, mouse. I started out with your run of the mill best buy keyboard and mouse but now I have a Corsair K65 RGB, Roccat Kone, and a Razer USB 7.1 Chroma. Peripherals are not necessary but they add an aesthetic appeal to your build.
PM me if you need some more advice or suggestions