The price for 1/2 liter beer in a grocery store will normally vary between 300 HUF and 500 HUF, depending on the actual store and whether they have any discounts available or not.
A bottle of Heineken (or a can) of half a liter currently costs 400 HUF in Auchan, one of the most popular and cheapest stores for groceries in Budapest, meaning that it is approximately 1,15 euros. Things change quickly, so who knows whether the prices will continue upwards due to inflation, or if they might stagnate and maybe even decrease in the future.
All in all, you will normally pay between 300-500 HUF for a can of 0,5L beer in Budapest in a normal grocery store.