Looking for a unique partnership with WP plugin developer

Am looking for a unique partnership with a WordPress plugin developer where the developer will create a plugin then i’ll pay in weekly installments the agreed amount - rather than the normal arrangement where everything is paid upfront. The plugin is a calculator that extends the functionality of the free plugin MyCred.
The reason am seeking this solution is because i don’t have the lump sum amount and waiting until I accumulate the total funds may lead to a lost opportunity.