Topic notes. Movement two addresses the conflict of interest directly, which is the thing that makes this sermon believable.
Three texts, three costs
choose one[Mark 12 is the risky one - see movement three]
2 Corinthians 9:6-15. Cheerful giver, sowing and reaping. The standard text and the one most likely to slide towards transaction if you are not careful with the sowing metaphor.
Acts 2:42-47 and 4:32-35. The early church holding things in common. Costs you comfort, because it describes something considerably more radical than an offering plate.
Mark 12:41-44. The widow's two coins. Read the surrounding verses before you decide: the passage immediately before is a condemnation of scribes who devour widows' houses, and the one after is about the temple being destroyed.
Say the conflict out loud
first minute[this buys you the rest of the sermon]
I am about to talk about money, and some of what you give pays my salary. That is an awkward thing and I would rather say it than have you thinking it for twenty minutes.
[then say what you personally give, as a proportion rather than a number, if you are willing - it changes the room]
The widow's mite problem
the honest reading[it may be a lament, not a commendation]
The passage is usually preached as praise for sacrificial giving. Read in context it can equally be read as a lament: a poor woman giving everything she had to an institution that Jesus says in the very next breath is about to be torn down, immediately after he condemns its leaders for exploiting widows.
You do not have to settle which reading is right. But using this passage to encourage people on low incomes to give more, without ever mentioning the second reading, is worth thinking hard about.
An angle worth taking
if you want it[the sermon nobody expects]
Preach a giving sermon that tells some people to give less. Anyone giving out of guilt, or beyond what their household can carry, or to buy standing in the room, should stop. A congregation that hears that will trust everything else you say about money.