I know this sounds over the top, but every year for our anniversary (in June) we make lobster thermidor, and I look forward to it all year! Really not complicated, use Hugh FW's recipe from his Fish Book. We have a fantastic cheap fishmonger and do go the whole hog by ordering a live lobster (about 25 quid for large one), freeze for 2 hrs to send to sleep humanely, then boil for about 15 mins. Split lengthways, chop up tail and claw meat. Add to sauce (which can do the day before) - basically tarted up cheese sauce with sauteed shallots, reduced white wine, lemon zest, mustard and gruyere cheese, and good amount of cream to a basic white sauce. Stir into lobster and stick in hot oven (if have let cool in advance) or hot grill with bit of extra cheese on top.
Have also made with ready-cooked fresh lobster from M&S and frozen from Lidl, and was still delicious. I realise not all comfortable with cooking live lobster (dh has to leave the house to take dog for walk whilst I do this bit!
We eat with a green salad. This year, due to greed of pregnancy, I did put in an order for some of dh's string chips cooked in beef dripping which were dee-licious on the side.
No need for cooked starter as pretty filling-maybe nibbly bits of olives/nuts/ parma ham etc with a G&T. Pink bubbly with lobster (the colour just seems right!) -Prosecco or NZ Lindauerfor my preference. Raspberry creme brulee for dessert. Nice candles and few flowers.
You'll never eat better meal in a restaurant, 50 quid budget or not! Mind you can't remember last meal out in eve we had as are both obsessive cooks and too wussy to leave dd and soon to be ds (and the dog). Also can eat meal in pyjamas if wished