extra money to thank someone (for example a waiter) for a service
a tip
have a value of
be worth
money that's paid back to you (for example, if you return something to a shop)
a refund
having a very high value
valuable
something you get at a really good price
a bargain
not worth its price
not good value for money
to need to pay someone
to owe
money that you get for doing something helpful (for example, finding something that was lost)
a reward
money taken away from the original price
$*off
available at a good price (usually for a short time)
on offer