Hi Mag,
Welcome to cr0! I'm sure you'll notice a massive difference to your curries in fairly short order. I got Khris Dhillon's book and thought I was doing reasonably well. Then I found this site, and I realized how much better it could get.
Luckily, onions by the kilo aren't that expensive, but yes, you'll be needing a lot of them--and you might want to put in one of those industrial vegetable oil holding tanks in your back garden too! ;D
Good luck with your recipes!
Cheers,
ast