I recommend a weekend away; somewhere quiet & scenic, at a 5-star B&B.
I took my wife to
this one for our first wedding anniversary. It's in deepest, darkest Derbyshire. She loved it. £100 per night, so it's easily within your budget. We stayed in the Dovedale room. Food was fantastic, and the entire area was so quiet you could hear a pin drop.
The village of Ashbourne is nearby, where I strongly recommend that you dine at a restaurant called
Lamplight (excellent service, food and prices).