Congratulations on becoming a mk3 golf owner. You will now learn more about cars than you thought humanely possible.
Timing belt intervals are usually 60000miles or up to five years...whichever comes first...people drive around without changing them...some get lucky and go 250000 miles with no problems, others suffer from engine damage.
It is not hard to learn there are plenty of guides here on the forum. Once you can do this job, you will know your car quite well. First time you do it it may take awhile..you may not do it perfectly and you will have to redo it, but if you follow the guide then you shouldn't damage your engine.
If you want someone else to do it, you may find that most garages will charge you two hours labour and parts. You will need the belt and tensioner, which are inexpensive.
I have seen mechanics who know what they are doing change it in less than an hour at a leisurely pace.
You wont need a lot of tools and I have seen it done an easy way by moving the alternator out of the way and then putting it back.
So a garden mechanic who is quick may do it for £50 with you supplying the parts. Think garages will charge you around double if not more. Considering the value of the car, you would be best off doing it yourself or having someone teach you how to do it. Try your luck on the forum here, maybe someone lives close to you or you are willing to drive out to them...and you can negotiate how they will be compensated for their time. Plenty of people have helped me out on this forum and thanks everyone. I am sure you will find someone to give you a hand.