Quick calculations with a pass :
- 254€ (286 USD) 4 day Global Pass
- 30€ Eurostar London - Paris
- 30€ TGV Paris - Turin
- 13€ Frecciarossa Turin - Rome
Total : 327€ including day trip to Normandy
This could be reduced to 307€ by crossing Switzerland en route to Rome (slightly longer with more connections though).
Regular tickets :
- about 125€ Eurostar London - Paris
- about 150€ Frecciarossa Paris - Milan - Rome
Total : about 275€ (Normandy not included)
Now if you were to go via the Bernina Railway (if you have time it'd be a fantastic experience), a pass would absolutely be worth the cost.
- 254€ 4 day Global Pass
- 30€ Eurostar London - Paris
- 10-20€ TGV Paris - Strasbourg
- 13€ Frecciarossa Milan - Rome
Total : 307-317€ including scenic railways ! The journey would need to be done in 2 days though.