Ignition module issues

I have a 1999 Subaru Outback with about 195,000 miles.  It's always run great except the check engine light started going on and literally 30 seconds to a minute later, the car would die.  All I had to do was restart it, the light would go off, and the car ran fine for a couple more days until it did the same thing again.  (It happens mostly when I slow down abruptly or let the RPMs get below 2500 following a downshift).  The accessory lights (like on the heater buttons) are dim and often don't even light up anymore.  The most recent issue is that I will hear faint "click" and the car will gain horsepower, then it will click again and will lose horsepower.  This tends to happen several times within a minute, and it happens without any change in my pressure on the gas pedal.  My speedometer also dies all the time and randomly bounces up to speed and back to o MPH constantly during drives.  Possibly ignition module?  I have to make an 8 hour round trip drive in a few days, so is this something that should be taken care of ASAP?  And how expensive can this replacement get?
Thank you!