Buy an older aeroplane and rebuild it.
If there is enough value in an equivalent already built plane then this is worth doing.
In your case you will end up with a plane which is quite close to a capable IFR tourer which if it was on the market now would go for about £250k. A used one would probably sell for £150k. A 2002 TB20 would now sell for about £150k (actual figure based on actual recent sales).
For fun, I looked at some old-dog TB20s which you can pick up for about £40k (probably nearer to 30k) with runout engines. You can get a new exchange Lyco for about $30-35k. Then install a G500+GNS530W from scratch, chucking away most of the old avionics (they will be useless anyway). Respray down to bare metal etc etc. Total cost will be about £100-120k and for that you will have a virtually new plane. Against buying one for £140-150k, this appears a marginal project, but if you know a really good engineering company which can do the lot in-house, and you like to micro-manage it, it would be worth doing because you will have a new engine, new (relevant) avionics, and everything relevant will be a known quantity. It would take about a year. I know somebody who did this on a 421C at Airtime in Bournemouth but a) a 421C is big enough to make it worth doing this on and b) Airtime could (at the time, anyway) do the whole lot in-house.
One doesn't need SV; all real IFR is done using standard techniques like published approaches.