I am interested in helping you with this task and can start now. I would finish the project in the time and budgets specified. I has installed for several companies (manufacturing/commercial/distribution/services) a web enable, light weight, modular and open source PHP/MySql ERP system, it is easy to install, configure and customize. It includes invoicing, inventory, receivable, payable, accounting, manufacturing, purchasing and can connect with any e-commerce system. I can add as many modules or programs as you request. Users can be defined with access to only certain options using a role based model. The time required to productions will depends on availability of data and functions desired (clients, items, accounting plan, suppliers, tax information, business rules, etc). After analyzing your proposal, basically the first part is already included in the options. Therefore, the project could be divide into three phases, 1. install and configure the core application, 2. make some adjustment to meet your first business needs and develop an integrated the second business requirement. Test all together and launch in production (5 to 7 weeks).
Feel free to contact me with any question.