There are many ways to approach this.

My way...

1) Set high fees, so only successful, well informed folks inquire.

2) Never haggle. Period.

3) Charge for client vetting/onboarding + name your offer something spiffy... like...

4) Advanced Practice: Have no front facing Website, so only direct referrals even know you exist.

I run a high traffic, high speed, private WordPress hosting service.

Recently a buddy of mine suggested I monetize my onboarding + his suggestion was good.

Now I'm doing Website audits, which I use to do for free, for $497 + affiliates who mail/promote my service are paid 50%.

So, I pay $0 for unlimited leads (OPML - Other People's Mailing Lists) + $0 for lead technology like mailing + then make $150 for every new lead... so think about this...

Every new lead pays me $150 each, so my lead generation is now a profit center, rather than time drain.

Try some variation of this where you...

Roll up your common practices/questions/activities related to onboarding into a sale or fixed priced (one shot) offering.