where's the cheapest way to get a professional website?

For someone who needs a nice website fast.

do it yourself, with WP ?

Either pay for it or do it yourself.

Purchase a WordPress theme and import its demo settings

Cheapst way : learn how to do it.
Fastest way : pay for it.

Not a correct combination: choose one.

Nerva said:

Purchase a WordPress theme and import its demo settings

Click to expand...

This is the right answer.

You just need to know basic wordpress things and rock and roll.

Very cheap and fast: use something like weebly or jimdo.
But thats something you normally don't want to do because the result is going to be crap.

Wordpress is in general cheap, but it takes some time to learn and adapt it. But its worth the time.

One can usually only have 2 of 3 common desires with any project. Good, Fast, Cheap. Rarely can you have all 3.

If you want something to be good and fast, it most likely won't be cheap.
If you want something to be fast and cheap, it probably won't be that good.
If you want something to be good and cheap, it will take some time to get it right.

You will have to choose which of these scenarios is best for your situation and act accordingly.
Either hire a pro, or do it yourself, if you want it to be good, it won't be fast until you become proficient with your skills.

I would probably take the time to do it good while also gaining a skill, but of course it's up to you. Good luck.