Hello, looking at your screen shot I see a number of features that need to be considered and will take a reasonable amount of work, well beyond the budget range you have.
Relevant Skills and Experience
I have developed a number of WYSIWYG editors in the past, both in flash and html 5. Primarily as internal tools. I have excellent development and architecture skills.
Proposed Milestones
$200 USD - Technical and aesthetic demo to be signed off on.
$466 USD - completion
Additional Services Offered
$800 USD - server side saving of creations with the app and a simple user system.
Not sure if the other bidders are underestimating the scope of this project, or bidding low to win the bid and then adjust to a fair price for the work and time required to complete this properly. What I deliver will be rock solid and easily extendable for any developer should you require additional features.