Kiltie
You need to think hard about this, in terms of your desired capability.
If you want european airways, note that for the UK you have to have an ADF, and for most places you need a DME. You also need a *BRNAV approved* IFR GPS installation, which is more than just screwing in an "IFR GPS" like a 430.
The GNS430 is a great deal for avionics shops but to the user it offers a tiny moving map, and your situational awareness is mostly from the moving map.
A KNS80 is a total waste of time because while it can be BRNAV certified it won't be much actual use in airways flying because ATC often give you a DCT to a VOR which is much too far away. A KNS80 won't work in that situation; it just becomes a very bukly DME. The only way to meet the nav requirement is with a GPS.
I will PM you some extra into.