A lot of older gear was designed for 1.5V alkalines and doesn't get along with 1.2V rechargeables. Expensive and wasteful to say the least.

External Pack:
Sometimes equipment has an external power jack (for wall warts) that will accept a higher voltage.

If you can wire up an external battery pack made of rechargeables with roughly the right voltage, you can save a bundle. You can always add a small value 1-watt resistor (cheap) if you need to drop the voltage a little.

Reuse:
The problem with reusing alkalines is leakage: as the voltage declines, the likelihood of leakage goes way up. Especially when they sit.

The simplest reuse option I've found is to "digest" them using cheap battery holders off eBay and use the old alkalines in LED lanterns or old big-body flashlights with those 6V square batteries.

You can get holders for any number of AA cells. If you can match the voltages of the used alkalines fairly closely, you'll get less leakage. And if it does leak, it's not in something you care deeply about.