"Is it normal to need to do lots of repairs on bikes?"
That's the 'piece of string' question!
Sounds like you have been fairly lucky.
A lot depends on mileage and general quality of bike/components.
This is not directly related to price. Simple/traditional bikes can run for years with minimal attention, but multi-speed 'high end' bikes might need a lot more care to keep them in good condition.
This is one reason behind the fashion/craze/practicality rise of singlespeeds.
There have been various discussions on here about the desirability of regular maintenance and whether to 'replace when a bit worn' or 'run until it fails'!
Some of the issues here - Annual service costs? WARNING - there are some high mileage and also some 'expensive bicycle habit' people on here. There is also 'standard CCE thread drift'.
Cost is of course a good enough reason to do some of your own 'preventative maintenance' and DIY.
Basic basics are keep tyres blown up hard - easier to ride and wear less quickly.
The other things that deserve attentions are the brakes. Inevitably the blocks wear and the cables also stretch and they can become less effective. Simple/quick adjustment can be done on many bikes with the adjuster where the cables meets the brake levers.
If the gears stop working 'cleanly', a small turn of the knob where the cable meets the rear gear changer can make a BIG differences and give you a real sense of achievement!
If your bike is a main means of transport and you don't want to do too much yourself an annual service at your favourite bike shop will become routine.
And don't forget to oil your chain when it needs it.