I had a belt slip a couple of notches whilst travelling at 70.
ALL the valves hit the pistons so every stem bent & every crown was gouged.
That needed a complete new head. I found it much cheaper to buy a lump from the scrappy, strip it completely & clean it up.
If the timing belt snapped, chances are you may not have caused much damage & may even get away with simply replacing the belt (although life generally isn't that kind!). Replacing the belt is the cheapest option, I'd try that first - line all the marks up & give it a go, you'll have to buy a new belt if you're getting a new head anyway & even if you buy a 2nd hand lump, it's just as well to replace the belt.
There's been a couple of 1.9 diesel lumps on ebay recently for less than a grand