Our house was built in 1950. My parents bought it in 1979. However, the previous owners were required by the FHA to remove the water heater from the kitchen and put it into the basement, before the FHA loan could be approved. They dug down in the crawlspace basement and cinderblocked it off with a retaining wall. About 15' long, 3.5' tall and 4 feet wide. They put the water heater at one end and a makeshift open sump at the other end. So basically water runs all the way across the floor to get to the sump hole and falls directly into it. Over the years, an elevated central heat/air system was put in between the sump and water heater, as well. When it rains moderately for 2-3 days, water comes in considerably. During a 3-4 day rain, I have seen water flows of 90+ gallons being pumped out every 3 minutes or so.
Could I just cover the floor in 3/4" crushed gravel, put down some french drain pipes, cover it with more crushed gravel and cement over that or something? I would need to install a proper sump basin, as well. Not sure how up to code that would be, though. The area is too tight to dig a french drain at the base of the wall on the inside, and trying to do anything on the outside of the wall is also out of the question.
What is the best and cheapest way to fix this? I should note that sometime next spring, we plan to sell the house on kind of an as-is basis, but will likely have to go through a realtor.