Welcome to SI and sorry that you're joining us. First, I'd like to refer you to the posts pinned to the top of the page, as well as those with bull's eye icons. They have some very good information. Second, the Healing Library is full of great information, too. I've bumped the ones with bull's eye icons so they should be near the top of the page.
If he's interested in R (reconciliation), then please have him read How to Help Your Spouse Heal From Your Affair by Linda MacDonald. It's a little over 100 pages, but is nicely spaced and doesn't take long to read. He needs IC (individual counseling) to work on his why's and to become a safe partner. If he took somebody on a business trip or two, it's doubtful that nothing physical happened. If he has, then he needs to be tested for STDs/STIs, as do you.
For you, IC with a betrayal trauma specialist can be helpful. Bonus points if they also do infidelity trauma. Don't do CC (couples counseling) until you have healed. A CC is more for working on the relationship and infidelity is often treated under the unmet needs fallacy. The CC will shift some of the blame to you. The decision to cheat is 100% his choice.
extremely reluctant and refuses to have more transparency and disclosure regarding the frequency, money spent, and any other details to provide reassurance.
This is not showing remorse and accountability. Maybe shame, but he's not giving you information that you may need to heal. How can you heal or forgive if you don't know what you're forgiving? If he has cheated repeatedly, then he is a serial cheater and they are notoriously bad at sticking to the work to become a safe partner. I'm not saying that it can't be done, because we have some really great reformed waywards on the site. They'll be the first to tell you that it's a lot of hard work.
how to move towards full disclosure
Ask for a written timeline with dates, feelings, money spent, details as to what they did like dinner & movie, hotel, etc. Give a deadline for when you would like to have it completed, or he may string you along forever.
Good luck and keep posting.