Lucre was first introduced in Expansion Set 6 of the original Eon edition and in Mayfair's More Cosmic. The original Eon use of lucre was not that inspiring and while Mayfair tried to add more uses for lucre, their implementation was more complex than it had to be. This is my version, combining elements of the two. The following does not address any lucre powers. [Editorial comments are in brackets.]
Everybody starts the game with 5 lucre. [Up from 4 in the original Eon rules and down from Mayfair's seating-based allocation.]
At the start of your turn, take one lucre from the bank. You do not get another lucre if you make a second challenge. [Though I like the idea, used by Mayfair, that the number of lucre you receive is linked to the number of bases you have, it does not fit into the rule set I have created here. I think it would work as a lucre-power.]
At the start of a challenge, when you receive tokens from the warp, you may spend lucre to retrieve extra tokens from the warp. For each lucre you spend, return one token from the warp to a base or the cone.
At the start of a challenge, when you flip the destiny color, you may flip again for 3 lucre. The original flip is ignored.
All other lucre expenditures can occur at any time before cards are played. You do not have to follow timing rules and you can always spend lucre in reaction to what the other players do.
Any player can spend lucre at any time before cards are played, but only the offensive player may retrieve tokens from the warp or re-flip destiny.
You may spend lucre to draw cards from the deck. For each lucre you spend, draw a card from the deck. For an additional lucre, you may immediately discard this card. You may not discard other cards.
You may discard your entire hand for 4 lucre. You gain a new hand following standard rules. [Mayfair gave players the option to spend lucre to discard cards. Discarding a card when you have plenty of cards is not worth much. Discarding your last challenge card is worth a lot. So, rather than pay to discard specific cards, I just have players pay to get rid of their hand, which is almost always the point of discarding cards in the first place.]
You may spend lucre to increase your challenge total. Allies can also spend lucre to increase the challenge total of their side, but non-involved players cannot spend lucre on challenge totals. Each lucre spent adds 3 to your total. Lucre only adds to challenge totals when spent. [I do not like the idea of spending lucre to increase totals after cards are revealed; throwing money into war only works before the battle. There should also be a lucre-power that allows lucre to increase challenge totals without spending them, like Mayfair's Gnome.]
You may spend lucre to buy a flare from the unused flare deck. This costs 3 lucre. If using Mayfair flares, the cost is only 2 lucre.
You may spend lucre to replace your alien power for 10 lucre. The replacement power is drawn at random from the unused powers. If you receive Schizoid, redraw. In a multi-power game, it costs 10 lucre per power you wish to replace.
You may add another power to those you already possess for 20 lucre. The new power is drawn at random from the unused powers. If you receive Schizoid, redraw.
You may spend lucre to boost your power. For 4 lucre, you gain the benefits of your power's super flare for the remainder of the challenge. [I don't like the randomness of super flares. I like the idea of being able to use supers in a more predicable, strategic way.]
When receiving consolation, you may take one card or one lucre from your opponent per token you had in the challenge. If your opponent has no lucre, you are not obligated to take cards. You may immediately and freely discard any or all cards you receive in consolation. [Notice I say had in the challenge and not lost in the challenge; Zombie gets consolation without argument.]
When receiving defensive awards, you may take one card from the deck, one lucre from the bank, or one token from the warp for each token you had in the challenge. You may immediately and freely discard any or all cards you receive as rewards.
[I am of the opinion that drawing consolation or gaining defensive rewards should rarely hurt you. At worst, they give you no benefit. I have thus made both optional and gave the players the option to discard unwanted cards. Also, when I added the option to take lucre instead of cards, there had to be something to balance out lucre's flexibility; otherwise, players would rarely take cards. This way, if your ultimate goal is to get cards, it is slightly better to get cards as consolation or rewards than get lucre and then buy cards later.]