Hotel - I think the cheapest hotels (and we're talking dirt cheap motels, one step above a hostel) are going to run you about 50,000k won a night. a decent hotel will probably be around 60-100k won. AirBnB's can be cheaper or more expensive depending on the type of property and location
Taxi - Pretty cheap. the starting rate for a taxi is 3200 won and then from there they'll charge by distance. You can get to most places in seoul for under 20,000 won. Taxis are much more affordable in Korean than Ubers in the US for sure. Highly recommended if you need to get some place fast and you don't have the time to take public transportation. That being said, public transportation in seoul is really, really cheap too. you can get anywhere for about 1500 won. It's a flat rate and they don't charge by the distance. And that includes transfers from bus to subway too. You don't pay a remounting fee, you just tap your transportation card to transfer from one mode of transportation to another
Food/Water: again this is subjective and dependent on your tastes, but you can eat at a convenience store for 5k won or less (which would be like an onigiri and a cup ramen or a bento lunch box). Normally eating out at a restaurant in Korea will cost you between 8k-15k won depending on what you have. Assuming you eat two meals a day and you get snacks/coffee in between, it'll cost you about 20k-40k a day on food expenses if you're not eating from the convenience store.
Translator - You can find a list of translators on PF here and they'll usually charge about 30k-60k and hour for their services. But from what I've seen on the other threads, translators can be hit or miss, especially if they're guys. There's a lack of contact info for female translators atm
Medical concierge/Medical tourism agency: I always plug
Medical Avenue and
Seoul Guide Medical cause they speak english (foreigner owned) AND (most importantly) they're FREE to use. With these agencies, they don't get paid unless you book a tour and their revenue comes from the government/clinics so you don't have to pay them anything to use their services which is amazing. Definitely give them a shot. I'd recommend them over using a translator cause with translators usually you have to pay them by the hour, up front and they're usually just one person shops which can be sketchy too