Broken Charger, Intermittent Charge when shut down

I recently began having a problem with my charger that came out of the blue. It had been working fine for the year and four months that I have had a Macbook Pro.

When I plugged in my charger one day last week, the led light began to blink green once every few seconds. So I reset my computer to no avail. I reset the PRAM, and that didn't work either.

However, when I shut the computer down and plug in the charger, it will charge for minutes at a time, and then blink and begin charging again a few seconds later. It does take quite a long time to fully charge the computer, over 8 hours.

I have tried a friend's charger that worked perfectly fine.

I'm not sure exactly what to do, because I am out of warranty. If I take it into the Apple store, they're probably going to tell me to buy another, and I really don't want to drop $80 when my computer will charge when shut down. Is there any way to fix this? or do you think I would be best off taking it to the Apple store and seeing what they say?