Honestly, I have a hard time recommending any "cheap" GPS these days. If you're putting it in the panel, it makes sense to get it IFR certified. Otherwise, as mentioned in the thread, there's not much point to it anymore. Having chosen to put a GPS in the panel, there are a few new choices, none cheap and really only one used choice that makes sense, also not cheap. In the used "cheap" market lie the KLN and Apollo units. Both have the same problem: extremely limited data cards and highly compromised support. They aren't going to have much life left to them before all support is ended. They also both have data cards that are no longer in production, with the companies desperately recycling cards to extend the life. After you've paid the considerable labor to have them installed in your panel, generally exceeding the cost of the unit, you won't have something that is particularly useful in the panel and won't raise the value of the plane.
In the used market, there is really only one unit worth looking at, and that's the Garmin GNS series. The used prices reflect this, as they're more than half the cost of a brand-new GTN. The non-WAAS units are ending support, so that really leaves you with only the WAAS units. And they're pricey. However, they're functional. They'll do nearly everything the GTN series will do, just without the sharp screen or easy interface. You'll be twiddling knobs instead of taping. WAAS also has the advantage of feeding an ADS-B transponder, saving the cost of an internal GPS receiver in whatever unit you choose, should you go that route.
In the new market, you've got Garmin and you've got Avidyne, both expensive. Bendix/King is in the market, but their unit is crap. I believe the Garmin unit is better, and that's what I installed in my plane. Others like the hard buttons of the Avidyne, but I didn't like the smaller screen and lower integration with my portable electronics.
If it were up to me, I think the best bang-for-the-buck (though hardly cheapest) choice would be to leave your radios alone. Buy and install a Garmin GTN-625 (GPS-only, no nav, no comm). Buy and install a Garmin G5 HSI. (You need an indicator to make it IFR legal and the G5 is not much more than a stand-alone indicator but provides far more function.) About $15,000 all-in. Yeah, it's 3X the price of a "cheap" GPS installed, which would be about $5,000. However, it's a one to two decade solution over a stopgap measure.
I have used them all. My favorite is the Garmin 696. I also have my Ipad Pro 10.5 with wing X. I put the 696 in my radio stack section of the 172.
