It is very important in Netrunner to be able to pay for the cards you want to play. You pay using credits and you can get one credit by spending a click.
This is far too slow, so you will want to put economy cards in your deck to give you credits faster than this.
There are several different cards that give you credits, and they all work slightly differently.
It is possible to compare them if you consider that 1 click is equal to 1 credit. 1 click is also equal to 1 card, as you can spend a click to draw a card. Making a run also costs 1 click, so that is another comparable ‘unit’ of value.
The basic action of spending a click to get one credit is therefore 1 for 1, breaking even.
An equivalent card would need to cost 0 credits and return 2 credits. This is because it costs a click to play the card, plus you had to draw the card in the first place, so the cost is ‘2’ and the return is 2, which will break even just like the click action.
Now lets look at some runner economy cards:
Sure Gamble costs 5 credits and returns 9 credits, so the ‘cost’ is 2 + 5 = 7 and the return is 9, you the profit is 2 credits.
Armitage Codebusting costs 1 credit plus you have to spend 6 clicks to pay out 2 credits each time. The overall ‘cost’ is therefore 2 + 1 + 6 = 9, and the return is 12, so the profit is 3 credits.
Daily Casts costs 3 credits to play and pays out 8 credits over four turns, so that is 2 + 3 = 5 returning 8 which is again a profit of 3.
Dirty Laundry costs 2 to play, gives you a run action and pays 5 if you run successfully. This will be 2 + 2 = 4 and paying back 5 and a run = 6, which is a profit of 2 (plus whatever you got from the run).
Professional Contacts is interesting as it costs 5 to play and you spend a click to return 1 credit and 1 card, which is a payback of 2 units per click. This can go on forever, so the profit increases the more you use it.
After 1 click, the cost is 2 + 5 + 1 = 8 and the return is 2, which is -6 and is pretty bad. After 5 uses, the cost is 2 + 5 + 5 = 12 and the return is 5 x 2 = 10 which is now only -2. After 7 uses, you break even with 2 + 5 + 7 = 14 vs 7 x 2 = 14. From then on the profit grows.
Magnum Opus is virtually the same as Professional Contacts, as it also costs 5 and returns 2 credits per click. It will show a profit after 7 uses. The difference is the Opus is a program requiring 2 memory units which can be awkward. The Contacts is a resource, which doesn’t cost memory but can possibly be trashed. Also, drawing a card each time is not exactly the same as having money to spend on breakers, and the extra cards can clog up your hand.
Economy cards tend to be classified into either ‘burst’ or ‘drip’ and typically only one type works with a particular deck. If your deck is constantly spending to make runs on servers and you are nearly always out of funds, then a burst economy card, such as Sure Gamble, will be less useful as you will seldom have the 5 credits up front to pay for it. In this kind of deck a low-cost drip economy, such as Armitage Codebusting, is better.
There are other runner economy cards, and further different ones for the corp, and comparing with this cost/profit calculation can help you evaluate which would be better in your deck.