Source: https://xcom.fandom.com/wiki/XCOM_Funding
Timestamp: 2019-04-18 11:06:57+00:00

Document:
Funding for XCOM is provided each month by the Council. These distributions coincide with the monthly Council report and consist of rewards of cash funding as well as additional scientists and engineers. XCOM earns these monthly rewards based primarily on the satellite coverage over individual members; these rewards are detailed in the chart below.
The starting funding and the monthly reward XCOM receives combines a basic funding amount based on difficulty level (see the table on the right) with the funding gained from satellite coverage (the country in which XCOM headquarters is located starts with a satellite overhead).
The amount of starting and monthly funds received from satellite coverage are also adjusted according to difficulty level as shown in the table on the right.
Base Funding values vary upon difficulty levels and are §175 (Easy & Normal), §75 (Classic) and §50 (Impossible).
The Africa continental bonus further increases this value by 30%.
Country Funding values are §180 (North America), §100 (Europe & Asia), §130 (Africa, including 30% continental bonus) and §80 (South America).
On Easy difficulty the values are increased by 50% to §270 (North America), §150 (Europe & Asia), §195 Africa, including 30% continental bonus) and §120 (South America).
Second Wave's option New Economy will affect this starting value.
HQ Starting Money has a fixed value of §100 for all difficulty levels and is given once upon game start.
Facility Maintenance: 1 Access Lift (§10), 1 Satellite Uplink (§15), and on Easy/Normal difficulties, 1 Officer Training School (§25).
Craft Maintenance: 2 Interceptors and 1 Skyranger (§20 each, total §60 - the North America continental bonus reduces it to §30).
The bold country is where the base will be located if you pick that continent to start the campaign.
↑ The country in bold is the base's starting location, and determined by the continent that is chosen when starting the game.
↑ These are totals based on the number of satellites per continent, and are not cumulative. For example, having 2 satellites in Asia on Easy/Normal provides 3 engineers, not 5.
↑ The base's starting location automatically grants it that continent's bonus. If all the Council members on a continent are covered by satellites, XCOM gains that bonus as well.
Base Funding which is the general income given by the Council (varies based on difficulty level).
Country Funding, which is only given if the country has a satellite deployed over it. The values are fixed and listed below, unless Second Wave's option New Economy, which will randomize the values.
A few Second Wave options can be enabled to modify or randomize XCOM funding.
Funding for each nation is adjusted on a monthly basis. This option is unlocked by completing the game on Classic difficulty.
Council funding steadily decreases over time, eventually reaching §0. This leaves very few options to earn credits, including mission rewards and selling alien artifacts at the Gray Market. This option is unlocked by completing the game on Impossible difficulty.
The starting aircraft (Interceptor, Skyranger) have a monthly maintenance cost of §20, while the Firestorm has a cost of §10. This value can be reduced by 50% with the North American continental bonus.
The total monthly income at the disposal of the Commander to purchase/build/hire is calculating by subtracting Expenses from Gross Income. This value may be negative, in which case you'll receive a warning message.
It is possible to run a negative budget, but if you ran out of available credits your balance will go negative. If you have negative funds, you'll have to repay the value before you are able to purchase, build or hire. Ending the month with a negative balance will reduce the grade received in the Monthly Report.

References: §175
 §75
 §50
 §180
 §100
 §130
 §80
 §270
 §150
 §195
 §120
 §100
 §60
 §30
 §0
 §20
 §10