What is the cost of a mailing list for email marketing?
It varies, massively. Some businesses, like luxury travel companies, spend hundreds of thousands of dollars on pre-made lists, or paying affiliates to gather leads for them. You can get started on your own list and build it up over time for the cost of a coffee mug. How?

Email marketing is an online marketing strategy that has the capability of driving more than 35% of the total sales for a business if you do that in the right manner. According to how you worded your question, it seems as if you are seeking to purchase a mailing list for which I strongly suggest not doing. I have been into digital marketing for several years and buying lists is a massive risk with little chance of a reward, especially for a beginner. I can, however, give you many suggestions about building an effective email list. I am pleased to share with you what I’ve learned, from building and operating many successful email marketing campaigns.
Initially, when I started, I carried out my first campaign for a client with a list of leads that I later found out they had purchased, not gathered organically. Honestly, the list proved to be a total waste. It’s not that it gave ZERO results, but the engagement really wasn’t there.
At first, I thought my job would only ever be writing email campaigns for clients who already had a good list of their own. But eventually, I realized that I had to expand my skillset into list building for clients since many of them did not have that side of their business handled on their own. It sounds crazy to me, but that’s reality.
Although building from scratch was no picnic, the results were far better. A ready-made list can undoubtedly give a lot of subscribers, and that number might seem appealing, but it seriously hurts engagement, because no one likes getting emails from somebody they don’t recall subscribing to of their own accord. This isn’t even counting that most email services can detect bought lists and will put the hammer down on your account for violating email consent laws.
After a lot of research on email marketing, my suggestion would include building a list from scratch by using List Warrior(LW) or any other specific method. I am using LW these days. It is a several-hour-long video program teaching you how to build an email list in a way that costs nothing or little to nothing and adds up quickly.
In conclusion, I would recommend you build an email list of your own as it would cost less than getting a ready-made list. I got LW at the cost of a coffee mug. If you would be lucky enough, you can get that too at the same cost or even less.
Please feel free to reply to me in case you need more information on LW or any other point discussed in this answer.
Good Luck!
Thanks,
Cleo