I've done this before and to do a proper job it be very expensive, you'll be looking at around £500 for the inner parts alone. I bought my OEM GT bumper and grilles second hand so I don't have the parts list for those but the rest I had to get from TPS. This is the list I got from my invoice (price exc. VAT)...
1K0 121 283 F - Air Line - £6.71
1K0 121 284 F - Air Line - £6.71
1K0 807 889 B - Piece - £3.92
1K0 807 890 B - Piece - £3.92
1K5 807 248 B - Foam Insert for Crash Bar - £9.63
1K0 805 903 H 9B9 - Lower Bumper Spoiler - £41.86
1K0 807 093 D - Member - £47.27
1K0 805 588 S - GT Carrier (The big black thing that holds the headlights and bumper) - £206.33
1K5 807 109 E - Beam (or Crash Bar) £84.65
Total Cost inc VAT: £493.20
Additional Cosmetics - Not necessary but I had them on the list anyway so I put them up for reference.
* Primered Front Bumper Moulding (Under the lights, No headlight washers version)
1K0 807 717 B GRU
1K0 807 718 B GRU
= £28.34 inc VAT
* For cars with no fog lights but want to cover the gap with the proper flush lower GT grilles.
1K0 853 666 Q9 B9
1K0 853 665 AB 9B
= £61.68 exc VAT
But in all honesty I had two facelifted MK5's, one which was cut by the previous owner and I couldn't tell the difference visually. Save yourself some dough and cut off the excess or even let the bodyshop do it if you plan to get it resprayed.
