We just bought a stacking washer and dryer and now the electrical cord on the dryer won't reach down to the existing dryer outlet. Is there any way to convert a regular 3 prong outlet that is close enough into a dryer outlet?

You can buy dryer cords in different lengths at lowes/home depot/menards if the one you have isn't long enough. The longest one we carried when I worked at Menards was 6 ft. it would be a lot less work to replace the cord than converting the standard outlet you have to an outlet rated for a dryer because you would most likely have to rewire. A standard outlet is typically 15 amp, sometimes 20 but a dryer is usually 30 amps so the wire you have running to your standard outlet would have to be replaced with heavier gauge wire. Hope this helps.

A standard receptacle is only 15 or 20 amp 120 volt, with #14 or #12 wire.

A typical dryer needs a 30 amp 120/240 volt circuit, using min #10 wire.

So, the existing dryer outlet will need to be moved, and the cable extended, using the appropriate wiring method and junction box.

If this is an apartment, multidwelling building, or you rent, otherwise do not own a single family home, an electrician must be called in to do this.

You cannot convert a standard outlet.
Just have someone change the dryer cord to a longer one and save your money as ZoeMarie stated.