There are three possibilities here... First possibility is that was a quote from a Toyota dealer. They are quoting you a book rate and will be happy to charge you that. Second is that the shop is a small shop and, while the repair (engine removal and replacement with a used engine) might only take 10 hours, it will require that you bring your van into their garage bay and totally block that bay from use for almost 2 full days, meaning they can't get money from any other customer. As such, they need to take all their profit from you. A slight variation on this is that they really DON'T want to do that job, so they high bid it, figuring, if you pay the money, they'll be happy to take it. The third possibility is that someone, who has no idea what they're doing and have no capacity to do an engine swap estimated the cost of labor PLUS the cost of a new crate motor and then added 30% to the cost because they're going to call up another shop, provide the van and motor and take a profit on top of the actual repair bill.
In reality, the van is worth, at most, $7k ($8k if it's an XLE). There is no way it would be worth sinking $10-12k into it. Find an independent mechanic who will do the swap on a weekend. You drop it off on Friday at 4 and pick it up Monday morning with a LKQ engine dropped in. You're probably still looking at $2k for the engine and another $2-4k for the work. If you can find some car-guy buddies or have a friend with a lift (more likely to have all the tools/experience), you can probably do a swap in a weekend, with little experience, for pizza and beer. Another potential would be, if you access to military bases, you can often rent a bay in their Automotive Skills Shop (or automotive hobby shop) for a relatively small sum per day. There are usually guys there who can guide you through the work and/or help with the repair.