Well cut to the chase. The typical basic ground-up IFR avionics upgrade is going to approach, if not exceed, $20,000. This wont buy an autopilot or primary flight display, so youre stuck with steam gauges unless you can spend around $35,000.
Sadly, weve witnessed enough buyer remorse over the years when owners upgrade entry-level aircraft for IFR on the cheap. Whether its an unsupported IFR GPS found on eBay or passing on a PFD that can save money in the long term, its imperative to price all options before pulling the trigger on the upgrade, including pricing flagship packages.