Bribery

How much is a typical bribe? Depends how rich the recipient is, and what sort of exacerbating circumstances exist. Somebody will only take a bribe if they think they can get away with it.

If the recipient of the bribe is required to do more than nothing (such as beyond "you didn't see us"), multiply the value by 5.

If they’re really risking something, multiply it by 5 again. (x25)

If they’d hang for this, multiply it by 5 again. (x125)

If the GM wants to randomly add some person-to-person variance to this, they can determine how high or low the person getting bribed is willing to go, secretly roll 2d6:

2: This person is desperate and/or very sympathetic. -50% bribe cost.

3-5: This person is willing to take a low ball bribe. Might be sympathetic or not confident: -10% bribe cost.

6-8: This person is typical of someone in their position: Normal bribe cost.

9-11: This person is particularly scared of the consequences, thinks high of themselves, etc.: +10% bribe cost.

12: This person either has principles, hates you, or you're bribing a group of people instead of one: +50% bribe cost. Generally, if you underestimate how much the person getting bribed thinks they're worth, they’ll probably get offended and either extort you, outright refuse, or plan to double cross you. Similarly, you can do a secret roll if they low ball the bribe. If the bribe is too low, roll 2d6:

2: This person will take the bribe and then double cross you to the authorities. And they won't even keep the bribe, either out of principle or spite or loyalty or something.

3-4: This person will take the bribe and then double cross you. They'll keep the bribe, or a secret portion of it, and maybe give the rest to the authorities as proof. They just want to double down on the rewards.

5-6: This person will be annoyed and/or offended and ask you to stop bothering them.

7-10: This person will ask for a bigger bribe. If you low ball them again roll again.

11-12: This person will haggle with your bribe until they get something they think is reasonable.

(I use a silver standard in most of my campaigns, but I'll put this in terms of gp since that's typical of most other games.)

1gp will bribe a beggar.
10gp will bribe a peasant.
100gp will bribe a guard, acolyte, or tradesfolk of modest means.
1,000gp will bribe a merchant, priest, or tradesfolk of good means.
10,000gp will bribe a noble.
100,000gp will bribe a king. 
1,000,000gp will bribe a god.

For a beggar, a bribe will buy a few months worth of meals if you spread it out, or maybe some booze to go with it. You could buy some warm clothing, or a ticket out of this place.

For a peasant, a bribe could buy you a couple of farm animals to brace against starvation or get ahead. It could afford you a wedding dowry, and perhaps a set of nice clothes to go with it.

For a guard, a bribe means you can have some real fun: a couple of nights of prostitutes, higher end booze, drugs, and games. If you can get away with it, either by being clever or kicking back some of the bribe to your superiors, you could potentially invest in a nice home, or maybe enough goods to start a trade. Open an inn somewhere, or maybe own a windmill, or a big house in the country. Anything other than guarding.

For a merchant, a bribe can hire protection, either from legitimate guards or criminal gangs. Priests can afford luxuries. Tradesfolk can hire servants. All these folk can feel like nobles with a bribe.

For a noble, a bribe buys bribes. It's enough to fund fancy feasts and expensive outings to impress your peers and recruit knights to your house. This bribe could fund a small fleet of ships to better your wealth.

For a king, a bribe buys nobles. It's enough to hire an army of mercenaries, or outright purchase a county. It's enough to appease the people, for with this money one could lessen an extortive tax burden for a year.

For a god, a bribe buys glory and worshippers. A million gold is enough to erect a grand temple in their honor. Thousands of the finest cattle, libations, and goods can be purchased and sacrificed to your splendor. It buys oddities in abundance like golden statues laden with gemstones, albino oxen most fit for sacrifice, luxurious lifestyles for high priests and their cohorts.