Heavy Purse Achievement
Earn 5,000 Coins
For this you will have to have accumulated 5,000 coins within the game. This can be obtained in two ways. You will earn coins by popping pigs (this is only 1 coin at a time) and seems to be random, completing Wall of Pigs levels, and by earning stars to unlock coins. Completing Wall of Pigs levels and earning stars will be where you get the majority of your coins.
After gaining all other achievements I had roughly 2,500 coins. This is only half of what is needed and it will take 15-30 hours to grind out the rest. I personally chose Episode 1: Wall of Pigs Stage 5 as there are many pigs and all within the same direction as far as aiming your birds. Sometimes you won't earn any coins, but at times I was getting up to 7 coins.
NOTE: You can quit out of a stage and keep the coins you've earned. If you quit out and you still have a coin(s) that haven't popped out of their bubble, you will NOT get to keep those.
Another way is to buy coins with real money. This is the fastest way to earn coins, but it can be very expensive.
This will become easier if more levels are added to the game. Wikipedia shows 60-70 more levels that should come Winter/Spring 2015.