This sounds like Gemini type formed letters? Drilling into a metal building will be less effort than into a brick wall. Hopefully it's not some sort of stone with a random texture. Knowing what you are going to install these into will help. Do you have a hammer drill if its masonry? Allow 3-4 extra bits because those little ones break easily.
Let's assume you have the patterns and the letters already are drilled/tapped for the studs. TBH, this sounds like one guy for a long day with a bucket truck, assuming you are used to working up in the air and assuming you can drive right up to the wall. Also, allow at least two-three tubes of silicone for filling the holes. Go to the Gemini website and they'll have info on installing pin mounted plastic letters.
If you aren't used to working up in the air, then have them rent a 45' boom lift for you and someone to work out of. Call the local United Rentals, etc to get a cost on a lift. Get the quote in writing and make sure that the include delivery/pick, fuel, applicable tax, etc. They will give you a price of $xxx per day when you call, but it doesn't include everything.
In any case, make sure you wear a safety harness, gloves, goggles, etc while in the bucket up in the air. Getting a fine from OSHA will cost you far more than you will make on a bunch of these jobs.