Is it worth fixing?

I have a 1999 Dodge Grand Caravan with 155000 miles. I have a leak somewhere between the radiator and the overflow tank that I have been nursing for about a year. I also think the waterpump may be going and I am sure the timing belt needs to be changed. Electically, the interior lights work intermittantly and the speedometer is also intermittant. I have to admit, I have had few problems with the van and I actually am getting about 24mpg still. About how much can I expect to pay for repairs?