Looking for a single page checkout type module - Joomla! Forum - community, help and support

hi,

i'm setting patient portal medical office. we'd offer patients opportunity pay balances online.

i'm looking single page checkout. once patient registers , logs site, pull balance database. balance need pulled payment module.

i not selling product initially, want patient able pay balance.

eventually, might offer ability purchase allergy drops online.

i'm hoping module might exist, or might know how tweak existing module this.

thanks.