Depends on how the leads were generated + many other questions.
Read a few Dan Kennedy books or hire someone to help you.
For example, if you email a cold list of 60K email addresses, you're sending IP(s) + domain could be RBL'ed for a very long time.
If you send postcards to physical addresses, cost will be higher + you won't be RBL'ed.
Also important is first step of your marketing funnel, your lead magnet... then value loops various lead magnets suggest... then ascension paths to higher price point offerings.
Marketing is Marketing.
No difference between any niche/industry.
Same rules always apply.