I actually doubt it would meaningfully reduce food prices for regular consumers. Ukraine mostly produces bulk grain. The price of bread wheat hovers around 20-25 eurocent per kilo. When you buy bread in the store the cost of the wheat is a miniscule part of the price. The real money in the food network is not in farming food but in processing it and running grocery stores selling it. Wheat can easily triple in value just by grinding it to flour and putting it in a paper bag. The value of barley goes up over 1000% when brewed into beer. If we let Ukraine in maybe we can reduce the price of some grains and bulk sunflower seed by a couple eurocents which will make pretty much no difference at all for the consumer but it will reduce the profits of our EU grain farmers by double digit procentage points.

Can we counteract this with even more agricultural subsidies? Of course we can. But that's a cost that has to be planned for. The alternative is letting the least profitable farmers to go bust, leading to only mega farms remaining. Which is either a good thing or a bad thing depending on your perspective. Worth noting is that in Ukraine there are almost only mega farms already because of the Soviet farm collectivisation heritage. That's part of the reason they can produce grain so efficiently and cheaply, in combination with them having some of the most fertile soils on earth.