I'm toying with the same idea, and have also looked at going down the road of buying an FK2 which is not affordable (well to me anyway), as you say there is a shortfall of over 10K once all the mods are done and charger fitted. To me, if you want big power out of your car and want to keep the FN2 which many do so end up spending thousands to get more power, then a charger is the a good option cost wise. But figure in a good exhaust, header, CAI and LSD to be able to use the power. Then you have to stop it
I spoke with Paul at TDi-North about this and he recommended that you go for a charger with an inter-cooler and also have a decat header (4-2-1) with a 400 cel cat welded into the zort B pipe as the original cat tends to get destryed after time..
Reading on TTS web site, their kits (both inter-cooled and none) use the original pump and injectors (none IC sue original air box too), they say their none inter-cooler kit can also use the standard exhaust and cat with a gain of 100-bhp at the wheels which is impressive. The inter-cooler kits offer in between 300-450 BHP dependant on tune, at the the wheels (total, not extra).
It all depends on what you want and can afford, if you have the money go for a FK2, as like me who can't afford one. Then saving £5-6K and do as much of the fitting yourself if you can and you have a FK2 power equivalent car (not as good admittedly spec wise etc etc) for over £7k less then a second-hand FK2 (ATM), but most I see in Brum are going for 21-22K so that's £10-11K less making it more affordable for a powerful, FK2/S3 equivalent car. Plus a car you built yourself
. Modding these cars is a hobby too for most so going and buying an FK2 out of the box is not an option and then the modding of that starts and it never ends lol.
Good luck, keep us posted how you get on.
FYI - to insure an FK2 - sale price £21K is £30 a year cheaper to insure than my Modded FN2. Not sure how much extra an Super charged FN2 will be over what I pay now though. may make a call later out of interest.