It doesn't take significantly longer to get to Ronda (by bus) than to get to Malaga (by train); Ronda might even be a few minutes faster. And the Ronda ticket will probably be a good bit cheaper--though I can't be sure since I don't see promo rail prices at the moment. I've chosen Ronda rather than Malaga on two previous trips but will finally take the time to see Malaga next week. I've never felt there was a compelling reason to go, but with a lot of time available this year I'm going to check it out. Your situation is very different, and I would not prioritize Malaga.
My #1 recommendation for a day-trip from Seville would be Cordoba. It's one of Andalucia's three top cities, and it's a quick train trip from Seville.
I don't think Granada is a practical day-trip from Seville. Whether you take a bus or the train/bus combo, the trip takes about 4 hours each way. ViaMichelin.com estimates the driving time in your own car at almost 3 hours one-way, and that doesn't include stopping, getting lost, finding parking, or dealing with the car-rental agency twice. That wouldn't leave very much time to see Granada. I'm sure there are bus tours offered, but I don't know anything about them.
Spanish meal hours do not agree with me, so I don't have much experience paying for restaurant meals. I've seen lunchtime menu-del-dia offers as low as 10 euros and many more in the 10-20 euro range. Fancy restaurants will charge more, of course. And dinner prices are usually a la carte and substantially more costly. I think many people make a meal off of tapas, with the total cost depending on a lot of things, including how large an appetite they have, what they order to drink, whether the place is in a tourist area, etc. One example from today: I stopped at a multi-vendor market near the Plaza de Armas bus station and bought a large cup of cut-up strawberries and kiwi fruit for 4 euros. That seemed a bit high, but I have a lot of trouble finding vegetables in situations like that, so I was willing to pay for the fruit. I've paid between 1 euro and 2 euros for a bottle of water in restaurants on this trip
I've found food costs on Spain lower than those in Italy, but in Italy I don't have as much trouble finding side vegetables to order, so I probably eat more in Italian restaurants. I suspect you won't find food prices all that much higher in Spain than in Czechia, but I know nothing about alcohol prices.