Can you tell if it's an electrical problem or is the valve physically 'stuck'? Are you sure you're getting voltage to the coil? If it's a sticky valve it might be repairable. If it's a self contained item that's not servicable and is specifically made to fit you might be out of luck... WWV! Welcome to the World of Volvo (parts prices)
On our engine (not Volvo) the solenoid is embedded in the injector pump and looks like a special part.
Found this, perhaps on a larger Volvo but it may be similar.. this looks removable and cleanable.. but remember I'm no Volvo mechanic!