If you don't know this activity, you really should give it a try. It can be great fun and it has quite a lot of pedagogical value because your students are more likely to remember grammmatical pitfalls to avoid after having invested time and (make-believe) money in them. "Once bitten, twice shy" might be an appropriate idiom to explain the learning process.
How to do a sentence auction in your ESL class.
Prepare a handout, or write up on the board twelve sentences. These sentences should have some connection with something that you've been studying recently. In half the sentences, slip in some of the mistakes that your students often make.
If you have done much, many, some, any recently, mix in some sentences like:
*I don't have some money
I have no idea
*I have much baggage
You can lead in to this activity by asking your students if they know what an auction is and if they have ever bought anything at an auction. One easy way to explain what an auction is is to mention the online auction site, ebay. Someone is sure to have an anecdote about buying or selling something on ebay.
Tell your students that you're going to hold an auction, not for works of art or vintage cars, but for English sentences. Explain that some of the sentences are 'genuine', that is, are grammatically correct, and that others are 'fakes'.
Give them a budget, say, 4000€, and tell them that there is a reserve price of 100 and bidding must go up by at least 100€. By the way, you'll probably need to pre-teach this vocabulary.
Put them into pairs and give them ten minutes to decide which sentences they would like to buy. You will then play the role of the auctioneer, reading out each sentence and taking bids. If you are convincing enough when you read them out, some of your students who weren't going to bid will suddenly start having doubts and offering large amounts of money.
Keep a record on the board of which pair buys which sentences and how much was paid.
Only at the end of the auction should you tell them which ones were right and which ones were wrong. The winners are the pair who have bought the most correct sentences without losing money on incorrect sentences. Money lost on unwise purchases could be used as a tie-break.