Okay.... understood about the customer wanting cheap, but do you realize that acrylic is not really a good exterior choice for making signs ??
Up in a illuminated sign cabinet, they have room to expand and contract and the heat from the lamps helps keep them from breaking for the most part, but if you're going to fasten this down for outdoor use..... you should really look at other options and inform your customer that cheap doesn't always mean 'THE' cheapest thing on hand. If you're putting reflective on this, I'm sure it's some sort of permanent sign and even the drilling of holes and screwing it fast is a tricky adventure.