You are only required to have IFR certified navigation equipment necessary for the route being flown enroute, and the approach you are conducting at you point of landing. That means an SL30 is all you need at a minimum to legally fly IFR (at the lowest price point). You can?t do a GPS based approach with this, but you can do a VOR or ILS approach for your arrival. With nothing but an SL30, or something similar, you can still fly GPS enroute if you have a handheld GPS, or some other non-IFR approved GPS for the enroute portion, IF you are in a radar contact environment. If the ATC radar goes TU for some reason, you need to be able to revert to an enroute IFR approved navigation source (VOR in this case) for the remainder of the flight, and then be able to have the necessary equipment to conduct the approach at your destination (VOR or ILS in this case). Of course, this equipment doesn?t help with your looming ADSB requirement..
I dont have any VHF navigation equipment on my new RV8. I have a single screen G3X Touch, G5 backup, GNS 625 for my IFR navigation and ADSB source, and 2 Garmin GTR200/20R com radios (plus the required GTX45R ADSB transponder). Garmin offered - and still offers- a deal on the 625 when purchased with the G3X Touch. I can?t do an ILS, but that?s the only difference. The 625 is an IFR approved enroute and approach certified navigation instrument. I haven?t been to an airport yet that doesn?t offer an LPV approach to an ILS runway, with usually the same minimums as the ILS, and I can fly it coupled if I want, so any difference is transparent. I didn?t have to install a VOR/ILS antenna, and I can still fly enroute VOR navigation if I want to using my 625 (I don?t usually file that way, but I can). This panel, which I built, came with a price tag of around $23K a year ago. You can definitly do it cheaper with a VFR GPS, a Stratus for ADSB, and an SL30, but the functionality with a coupled autopilot makes IFR flying a little more comfortable if everything is integrated. Good luck with you choice. Be advised, most of us don?t do a huge amount of IFR flying, so spending tons of money to give you dispatch reliability like an airline is very expensive. I have personal minimums that would never require 200 & 1/2 ILS minimums, even though I could still legally do that with most LPV minimums. I just choose not to fly when the weather is forecast to be that low....