Brewster, not sure how much you're interested in the facts where they may conflict with your argument, but here goes anyway:
1. Garmin will upgrade (and fix everything else) on your non-WAAS 430 to make it WAAS. From their website:
List Price: $3,395 USD (subject to change without notice)
Visit an authorized Garmin sales and service center or call (866) 739-5687
Otherwise you can stay 129 compliant and buy a separate postion source such as the Freeflight 1201 - but that's going to cost you not much less than getting a TSO'd GPS.
2. A KT74 transponder is about $3500 (maybe a bit more with the exchange rate) but there are cheaper ones at about $2500 USD (Trig TT31).
So at a cost of $0 for the GPS changeover (*I'll qualify that by saying you need to have the right GPS antenna cable*) and a cost we paid of $1500 AUD installation (including an engineering order) on a Lance, you can do the whole job for just about than half of your $16k.
You still have the problem of finding alternates with only one GPS once all the aids are gone, that I can't help you with beyond saying that in any lighty, fuel reserves the nearest equiped aerodrome for most of the inhabited part of the continent still won't be unreasonable.
I'm also curious as to why you've dropped to NVFR about 8 months before needing to in WA and 18 months before the rest of the country needed it?
UTR