Now, this is probably a very simple problem, but I've been trying and didn't get to a good solution.
Say that there is the need of renting a house near a place, and we have a list of candidates. Of these houses we know their price per day and the distance from this place. What I would want to calculate is some kind of "convenience index", basically if an house costs less and has less distance (from the place) it will have a greater value, if costs more and it is more distant (from the place), it will have a lower value.
I think you need some kind of weighted average. Pick two numbers $a$ and $b$ and calculate $$ \text{inconvenience} = a \times \text{ cost } + b \times \text{ distance }. $$ The larger the value the less good the house. The larger $a$ is relative to $b$ the more cost matters compared to distance. You will have to pick values for $a$ and $b$ that make sense in context.