But there is a lot of really cheap equipment out there that may make it worth while.
As tempting as used commercial gear may seem, I would be especially cautious when selecting a portable radio.
My thinking is that as soon as it's known that certain radio models are no longer in service, there will be no more batteries made for those models.
While other high-wear parts, such as knobs, speaker-mike cords and antennas can be cannibalized from dysfunctional gear, batteries have a shelf life.
Time will tell if 3rd party manufacturers of batteries will continue to support obsolete equipment.
Some of that business decision could come from previous sales of certain batteries, which in turn goes back to the popularity of the model line itself, as well as popularity in the used radio market. Hams have probably contributed to continued battery availability through their purchases of batteries for their used commercial gear. I'm getting the feeling that the trend in amateur radio may be shifting away from used commercial gear, and toward cheap and lightweight Chinese portables.
For as long as the HT220 model has been out of production, batteries are still available to this day. That model line was popular for a couple decades. While the MT500 battery usually has a different part number, it's dimensions and voltage are the same as the HT220.
Even if a HT220/MT500 battery were to become unavailable, both radios still have the compartment and space to house a couple 9V transistor batteries.
A problem with more recent radios, such as an HT50, for example, use a battery that doubles as a rear housing for the radio. A person would need to carefully dissect this battery to remove/replace cells.
My advice in choosing a portable would be to look at the battery first. If the battery is interchangeable with another model that's narrow band compliant, then it's probably safe to assume that batteries will continue to be available for a while.