Yes, herb flowers are edible. Although it should be noted that not all herb flowers are edible and you can even grow them in your own garden even if you are on a tight budget.
Here are some of the herb flowers which you can grow and are also edible: Agastache foeniculum or anise Hyssop, Monarda or Bee balm, Borago officinalis or borage, Calendula, Allum sativum, Lavandula or lavender, Cymbopogon citratus or lemongrass, Tagetes spp or marigold, Mentha spp. or mint, Origanum spp or Oregano and Marjoram, Petroselinum crispum or parsley, Rosmarinus officinalis or rosemary, Salvia spp. or sage, Pelargonium spp or scented geranium, Thymus spp or thyme and Viola odorata or violet. There are a few more herb flowers and this list just contains some of the herb flowers that you can grow and eat.