Your questions are way too vague to be answered.
Ask more precise questions.
It is good idea to start web design service?
Depends.
If it is good, How much earning possible by providing web design service?
There's no definite answer to this question.
I know guys making hundreds of thousands (€) yearly, and I also know people who can't even get their first client.
Where we can get client for web design service?
Absolutely no one will answer this question precisely for you. At least for free.
Organic traffic works wonders for high ticket items.
How much money we need to invest for marketing to client fast?
Again, too vague questions.
For Google Ads, I wouldn't even bother starting any campaigns if I didn't have at least 5-10k€ to burn. Cost per Lead in web development in GAds is quite often in the thousands (€), at least in 1st tier countries.
What is the current market price for 1 wordpress website ?
You can purchase WordPress sites for as cheap as $25. That'll get you a site with nulled plugins and a cookie cutter theme that looks crap and unoriginal.
Then there is actual web development work that can easily range anywhere from 1k€ to 30k€, depending on the scope of the project.
Ask better questions and you might actually get answers that are useful.
