The title says it all. I'd like to know what would be the best and most affordable equipment for a person who would like to start learning guitars and bass. I have a microphone, but I do not have a stereo equipment to plug it in, as I had years before. What do you recommend?

That depends. Are you going to be recording or just practicing/playing gigs?

Just to practice, eventually, to start recording.

I would browse your local craigslist ads or reverb for a used Fender Squier or an entry level Ibanez RG series guitar. Both are simple to setup and maintain, and are well enough built to get you through the first couple of years after which you may want to look into other guitars that are built better, intonate well, etc. But if you're just starting out I wouldnt bother too much with a pricey professional instrument. You should focus on building muscle memory, training your ears, developing your fretting and picking techniques etc.

For amps, Id just try to find a used Line6 combo amp with the built in effects, or one of the newer Boss Katana practice amps. Again, the focus is on playing when your starting out, so you dont need to buy a half stack or some insane boutique pedals to get by. You could also use the combo amp that comes with the Fender Squier if you buy new and find a cheap multi-fx pedal from DigiTech, Line6 (used pods are cheap now), or Zoom.