Sewing your own dresses can be really rewarding, especially when you learn to make your own patterns. There is nothing more fun than designing your own clothes and being able to replicate styles you like that would be normally out of your price range.
If you need to purchase some fabric like silk or wool, which is much more expensive than something like cotton, I recommend trying to look through the discount bin at your local fabric shop. Often you can find pretty good size pieces of luxurious fabric at rock bottom prices. Have fun and buy some different pieces. Mixing and matching textures can have great results.