Abhi you can if you do it properly. What I mean by this is assume responsibility for the entire project - not just the website design, but the backup, database management, security, hardening, SEO / analytics etc.
Ordering a complete package for a competitive price can be very lucrative provided you hand over a WordPress build that is the envy of others in the same space as you. Create a product people actually want and need, rather then just designing the pretty front end and nothing else.
People like value for money and green they got a bargain when they get handed a system that is fast, secure, looks good, and most importantly of all, has a low administration footprint.
With all build I do, I also offer lifetime advice for free, but if that client wants extras outside of the original quote, they have to pay.