Don't buy your avionics till you are ready to install them in the plane. So much changes so fast. Also the warranty may start ticking. At this point you want to start looking, deciding on the brand, what components are needed, where they go in your plane, antennas, wiring routing, etc. If you are able I would suggest spending 2-3 days minimum at Oshkosh visiting Garmin, Dynon, MGL, etc. so you can see the products first hand.

Usually you can get the best price during the week of OSH, but you have all your fact finding done. When you are ready to buy them go to OSH again (maybe 1-3 years down the road). Research the prices from all of the big dealers for the entire package before you go so you know who can give you the best deal. Spend a day or two visiting the dealers at OSH and see what price they can give you for your package and be ready to write the check.

I have no regrets getting the Garmin G3X package and yes, I wish I didn't have to pay for database updates (you don't pay for software updates). I keep up to date with iPad with the Garmin Pilot app for $75 per year.

There is a lot more to consider than the $ for updates when choosing your panel:
-Ease of installation (but this is only done once, so don't get too hung up on this)
-Screen quality (resolution, view angle, glare, etc.)
-User friendly
-Variety of choices for screens
-Weight (shouldn't be a big difference)
-Do they have a transponder, autopilot, ADSB, COM, intercom, etc. too (if not how will it interface with the brand you choose)
-Presentation of information (can you pick where things go on the screen)
-Warranty, customer service, help desk, company reputation