Sorry to hear this shooter.
You will probably find the engine is not siezed. More likely one of the chains has snapped. The down side to this is you may have piston to valve contact and thus some bent valves.
On my engine when i had the rear chain snap as i shut it down i had a couple of slightly bent valves.
First off you need to whip off the cam covers to see if either of the cam chains is broken. If neither are then you will have to whip off the front timing cover as it will probably be the crank to jackshaft.
If the rear chain is bust then the engine will have to come out to sort or the tranny removed as you need to get access to the rear jackshaft bolt. If the front cam chain is bust this can be fixed in situ. the heads can be removed to sort the valves with the engine in. you will only have to remove the head for the side with the broken cam chain. If the main chain is bust then it is likely you will have bent valves on both heads.
Having typed all this you may be lucky and find all chains intact but one of the guides is in pieces and has wedged one of the sprockets.
If you are in need of the vehicle back on the road quickly then the best option is to drop a use lump in there and may work out cheaper than repair unless you can do all the work yourself.
Hit me up if you need any advice, you could also read some threads by 2000StreetRod
Edit Bad timing but i sold a partly reconned engine not long back for £230. If you pm chrisquelch he may have an engine.
If you decide to repair and it is the rear cassette i have one that i am prepared to sell tho you will need lots of other bits so you could probably buy them all together from the states.