There is a big difference in cost depending on whether you have a digital copy of the text or a printed book.
If you have a digital copy, freelancers will convert it to the formats you need for as little as $35, but the people I recommend start at $100 for the most basic manuscript (i.e. no pictures etc.). The more popular services charge around $200 and there is quite a wait time.
As it's an out of print book, you probably don't need an editor, but you might want to have it proofed - you will know best.
Aside from formatting costs (which you can do yourself if you want), proofing costs (if applicable), and a cover, that's it.
Any money you want to spend on marketing is up to you, but there aren't enough hours in the day to get through all the free options available.
However if you only have a print copy of the book, that will cost you a good bit extra because they have to scan it, then fix it all up, which is time-consuming.
Dave