Help and advice needed please.

Just had my final Lexus dealer service on my IS200SE with 102K on the clock.

Lexus advised they could not change the timing belt as the water pump was leaking (?!)

Does this make sense?

I don't want to pay the £800 Lexus are quoting to replace the water pump and timing belt.

Can I get it done cheaper some other way?

How many miles can I go before I really start risking the belt going.

Car does 500 miles/week mostly on motorways.....

my water pump leaks, most do. get your belt done asap IMHO. I had mine done at about 100k and was nearly gone
my mate did my timing belt for me for £50 + £20 belt + £45 tensioner pulley that had gone
don't use lexus they quoted me £350