I do put a mini bouquet in the guest room, in a sweet little pewter vase I got at the second hand store for a buck (if someone knocks it over onto the tile floor, it won't break, like my last pottery one did) all picked from my garden or along the road. Might just be a couple of flowers, a fern frond, some wild grasses, whatever happens to be growing at the time. Takes me about 2 minutes. I certainly wouldn't go out and spend money on flowers, though. And I never go in to refresh them during a guest stay, just think it's a nice touch when they arrive.
Have a friend who's really clever at thinking of creative ways to make $. She used to spend a couple hours on a Friday afternoon driving around the countryside, with a few 5 gallon pails part full of water and ice in the back of her car, pick whatever wildflowers, wild grasses, rosehips, whatever, shove them in the buckets, then get up early on Saturday morning, go to the farmers market, where she arranged them all into bouquets and would sell out in about an hour- made several hundred dollars every week and her only expense was the gas money and a couple hours of her time.