Okay, the only thing that the contract obligates the dealership to is give you a trade-in for $3,000 on the purchase of a new vehicle. Since the financing did not go through, they are not obligated to give you a trade-in, since you will not be purchasing a new vehicle. However, since the financing did not go through, you are not obligated to do business with them, either. The contract you signs talks about a trade-in, it doesn't say you're going to sell your van to them for the fair market value. Since they already sold your van, they can offer you the fair market value of your van, which they supposedly did (although I don't know what your van books for, you will have to check that). However, you don't have to accept this. If you research the fair market value (i.e. book the value on blue book, etc.) and find that the fair market value is higher than what they offered, you can go to the dealership and tell them why the value is higher and ask that they pay you the fair price.
If they refuse to pay you the fair price or if you would rather have your van back, then you can file a petition seeking the court to grant an order directing the dealership to give you your van back. However, please be aware that if this is impossible, the court may just order that the dealership pays you damages, which may include the fair market value of the van, costs you had to incur to obtain transportation while you had no vehicle, etc. Basically, the court will try to put you in the same position that you would have been if the transaction had never occurred.
If you are a low-income individual, you may qualify for free legal assistance in this matter. This site offers links to organizations which provide legal assistance in different states: www.ptla.org/links/services.htm. The issues in this case are somewaht complex, so I recommend that you seek assisstance from a local attorney who can give your their opinion of the viability of your claim as well as trends within your local courts.
Please let me know if you have any other questions. If I have answered your question, please click "accept."
Best wishes and good luck!