Custom PHP/AJAX programming for existing Joomla site

Hello, We need a custom article/form for an existing Joomla site. This must be a user form linked to an existing database. Must provide cascading dropdowns that populate according to other user selected dropdowns via AJAX, from database table. Must also provide validation (AJAX) and upon submitting, must link to Paypal and then write the user submitted data to database. We have a Paypal plugin already installed which can be used to provide this. In summary: two tables. One is a catalog, from which dropdowns and a couple of non-editable textboxes or labels must be filled. The other table stores the user submitted data. We need two forms: One english, one spanish. Identical funcionality. We can work closely to provide all english-spanish translations, requirements, etc. Project is for two forms, with 3, 4 dependent dropdowns, 2, 3 labels, (dropdowns and labels db-driven) and around 6-9 user-filled textboxes. Both forms are identical except for language, integrated into an already existing Joomla site, which preferrably must be loaded inside an already existing K2 article with loadposition, etc. Cheers!