Regardless of whether it would be a German timeline, some basic information would be useful. Is the country you are considering industrialized (USA, UK) or less industrialized (Italy, Japan)? Is it a land based country (Germany, USSR) or is it protected by water (USA, GB, Japan)? Is the country relatively rich and has easy access to financial markets or is it poor and in debt?
As an example, Germany was spending about 17% of their GDP in 1938 on their military by using some financing trickery (Mefo bonds) while the UK was spending about half that percentage - 8%. During wartime, those percentages of GDP go higher such as the US at 41%, the UK at 52% and Germany at over 60%. For the costs of weapon systems, they can be googled. For example, a M4 Sherman tank cost between $45k and $65k per unit (1945 US Dollars) depending on configuration per their Wiki page.
This page lists costs for infantry weapons, tanks and artillery for some countries.
EDIT: Also you can use this
list of lend lease equipment to the Soviets that has some weapon categories in it such as aircraft, ammunition and other items. Note that the US lend leased various other items such as $400 in lipstick, 13,328 teeth, and a single pipe, tobacco valued at $10.