With patience and discretion, one could grow the most magnificent flower garden with only $100 worth of seeds. Author and poet James Fenton brings the wisdom (and a highly evolved list of plants); you’ll need the patience.
As for the design of this flower garden, I insist on keeping it vague. A hundred varieties of flower might look cramped on a balcony, spectacular in a situation only one size up from there. For it is amazing what can be crammed into a small space. Conversely, it is amazing the number of plants that could, in theory, be raised from so large a number as a hundred packets of seed.