Cheap Liquid level sensors?

I am trying to make an automated coffee machine using a labview interface as the only user controls (other than changing the filters). The problem is that the user must be able to select the ammount of coffee brewed (by the cup), The problem is that the reservoir and carafe sensor need to return current values to the computer in order to control each stage, and all the sensors on the market are hundreds of dollars.

I can probably do this with a floating arm and variable resistor, but I am running out of time to come up with a conditioning circuit.

Any hints?

what do you need to condition it to?
if you are using floating device to move glider of the potentiometer
you can connect it directly to analog voltage input of your choice.
ranges like 1-5V and 0-10V are common. you just need stable
power source (5 or 10V).

How about something that weighs the cup??? That would be heaps easier to make, and probably more hygienic than having something in direct contact with the brew.