I personally don't think there's enough info in the OP to tell us a real number.
What needs to be done exactly?

- will you be asked to help giving purchase advice? Calculate ROI, look for PSU's, shelves, cooling,... Or is is just installing gear that has been bought by your customer?
- will you be asked to calculate the mining room's wiring, breakers,...
- will you only be giving advice, or will you physically help to setup shelves, install A/C,...

I'd personally see what would be asked of me, try to calculate the amount of time i'd spend on the project, and multiply it with a reasonable rate (about $30-$35/hour in my country for such a specific job). Like it has been said before: maybe you'll work for a lot less (depending on your country, and the fact if this is a continuous or a one-time job).

For example:
- finding out which miners to buy, factoring in the electricity rate, custom fees, shipping and handling, PSU's, looking for second hand miners,... About 2-3 hours???
- looking at the cabling, breakers, calculating the btu's for correct A/C... About 2-3 hours???
- setting up the room: impossible to say (does the room need to be cleared, does it need A/C, is the wiring OK, how about security,...)
- ...

With a little bit of self-study, research and reading, you can do this yourself. If you have someone else do it for you, you won't learn anything and will have to rely on others to fix issues as they arise. Believe me, issues will arise.

It will pay off in the long-run to know what you are doing.

Just my $.02.