This project looks exciting, and reminds me a bit of Memrise. I like the idea of a leveling system rather than their gardener game system. However, I am hard pressed to offer a perfect bid amount to put your project to rest, as I have no idea how much is done nor the quality of what has been done, and the scope of the project. Were I to bid on this from scratch, I would probably be looking for something in the range of $6k.
As it is, my bid is for 30 hours of work on my part. Some of that time would necessarily be spent reviewing the existing work. I look forward to working with you, and patiently await any questions you have for me, thanks!