Do you need to remove the disc rotor to replace a drive side spoke? Today I had a spoke break in the middle of a ride. I did notice it had a wobble but I don't have the experience to tell what's passable. Even new bikes can have a slight wobble. so I dismissed it. 

I was quoted £30 to replace the spoke and true it - the mechanic said he had to remove the cassette and rotor to replace a drive side spoke. 

Is this true or they're having a laugh? 

Should I replace myself? if I remember correctly this wheel has had a a spoke break on me before.
Yes, usually you have to remove both to get the spokes through, although not every time depending on the specific hub and rotor.

It's typical that wheels that break spokes are going to keep breaking them due to build or material quality issues or both. So which is the least painful between doing it yourself 16 or 32 times versus paying for it versus buying a new wheel or paying to get it rebuilt all at once is up to you.

If the bike/wheel is within a warranty period and it's having this issue, it's an especially good thing to use the warranty for because if they're breaking when still fairly new, it really may not stop until they're all replaced. I've rebuilt or replaced many such wheels.

Replacing spokes is low to moderate difficulty, depending on how messed up the wheel is once you're getting it true, but does have a lot of steps, so shop rates for it unfortunately tend to be something like what you're encountering.