Only the engine you now have will fit. As far as other engines (used) that will fit you will have to have the same filfth digit on the VIN on the dash. If it has the same as yours it will fit. Here where I live NW Arkansas used engines go for around $300-$500. You can get a used engine at the auto salvage. There are plenty of zx2 DOHC engines but not many Escort 2.0 SPI SOHC engines. Many boneyards will put it in for you for $300-$500.
You can get a remanufactured engine for about $2000 or a new engine from Ford for about $3500.