I'm gonna tell you the cheapest way. And i've been saying this over and over to people who want to 'extend' their range.
Its not about hitting the notes. Its about suiting the song to your normal range. Face it. If you want your voice to hit notes like Celine or Mariah, you'll burst your vocal chords open with guts everywhere. Its just not possible. Unless you spend lots and lots of money, and we know how stingy Singaporeans are, especially with the recession and everything. So here it is:
If you have a Karaoke or play it on a guitar/piano, change the key. Its that simple. Experiment the song with the different keys. Hell yeah it'll be tough, i promise you. But only at first. Here are some steps for a guitar. You'll need a capo:
1) Try the song out on its original key.
2) Capo 5 and play the song. Try and sing. Its ok if you have to sing an octave lower.
3) Try capo 4, 3, 2 and 1. Everytime you change, sing Baa Baa Black Sheep. This makes your ears and brain forget the previous key so you can start on a fresh key. Or Macarena, or Crazy in Love or Living La Vida Loca or anything la.
4) Try the capo levels till max of Capo 7. Cos Capo 8 is just an octave higher, so no point.
Hope that helps.
Someone sticky this post.