For the US, if you are on budget, Arizona State University - Carey and University of Florida - Hough are free... and better than all the ones you listed
For the UK, Durham is the only one in your list that can compare with them

RoI depends on many factors including whether you have permission to work in the country. Generally, it's better to focus on NPV rather than RoI.

I do not currently have authorization to work in either country. :(

It's much easier to get permission to work in the UK than in the US.

See https://find-mba.com/board/general-forum/best-schools-for-international-students-placement-35651

In general I agree that a UK program would probably be a better option if you want to work in the country you study in.

Durham is the only UK program that you're looking at which is ranked in the FT. In that ranking, it doesn't show that it has great international mobility - in fact, among UK programs, it's the second worst for international mobility after Leeds. You'd have more success if you were able to aim a bit higher - Edinburgh, Imperial, Warwick, etc.

UCD Smurfit is also an option, if Ireland is on your list

I have authorization to work in the UK and I am also exploring affordable MBA options (full or part-time).

I am currently working in London and could continue to work while doing a part time program. However I could also take a year off and do a full time MBA at Brunel or another affordable option in or around London. If I'm not working it makes it hard to afford a better MBA.

I don't know what the best solution is. Please advise if possible.

Prioritising affordability gives the lowest return. The choice between full time and part time is determined by your career strategy. The bigger the move, the more you need full time. If you want MBA-type jobs, the added return on a great MBA will create huge added value. That's why loans exist for MBAs.

Loans and don't forget scholarships: the ticket prices for many of these programs are often offset, at least somewhat, by the funding offered on admit, especially for the most competitive candidates. Also, the schools will probably have a database of other funding opportunities you can apply for.

It's not always the case, but enough that you shouldn't be dissuaded by the actual sticker prices. It's at least something to look at critically, because the payoff in the long run would be worth it.

I think you've convinced me. I'll look at scholarships and loans to try to get into a better program. Beg, borrow, and steal, isn't that what they say? :)