I would not put a 18 year old car into a main Dealers, your going to be bent over and raped!

for 100K service I would expect

Brake fluid changed

£10 if you do it yourself
oil and filter change

£35 quid for decent semi synth and filter
fuel filter change

£ 7
hand brake tightened

- pig to do

- get them to do this
new brake pads and discs

(if needed)

- easy job

£200 quid though on parts for decent pads and discs
coolent change

-

£15 if you use generic concerntraite coolent and do it yourself

- chances are the dealer wont know how to do a MR2 correctly

Washer fluid top up

-

£3
Timming checked and Valve shimms adjusted to spec

££££

for

£350 if they are only replacing fluids then over 200 of that is labor!