We have never had much money when our kids were growing up and when it came their 18th birthdays they just had a slightly more expensive present but we went out for a celebration meal on top which we never normally did.
Now I look back and feel mean for not spending more at the time, even though I know we didn't have two pennies to rub together. I read so many posts on here about people spending hundreds on their kids birthdays and feel like this was just one more way I let my kids down!