If you want to go on the cheap, an (even less expensive) alternative to a "cruse control" is a mechanical (locking) hand throttle like I put in my CRX:
http://www.gassavers.org/showthread.php?t=4876
Pros:
It is cheap (under $35) to buy, and reasonably easy to install.
Unlike a cruse control, puts virtually no parasitic load on the engine, as it's all mechanical (and doesn't use electrical or other power to function, like a real cruse control does). The lack of parasitic losses for the controls, is a plus (vs a real cruse control) for FE.
This device makes it VERY EASY to accelerate slowly/smoothly, as you have much clearer feedback about your throttle position than your foot gives you. This is also good for FE.
You can easily switch back and forth between the hand throttle and the foot throttle. You can even use your foot to give you current hand throttle position a momentary boost (for climbing a hill, for example), as both throttle controls are hooked up all the time. So the one that "wins" at any given time, is whichever of your two throttles has the higher throttle position at that moment in time.
And the device makes it easy for you to lock a specific throttle position of your choice (i.e. a VERY EVEN "foot", as the mechanics stay in place)! This is also good for FE.
Cons:
The device maintains a constant throttle, not a constant speed. On level ground these are relatively the same (so the device works like a real nice "cruse control" on level ground). However, on hilly ground, I find myself constantly making minor changes to the throttle position (to keep my speed somewhat even).
And unlike a real cruse control, it will not automatically turn off when you step on the brakes (which could be considered a "safety issue"). However, this is mitigated by the fact that I have a manual transmission car. So if I somehow forget (in an "emergency") to turn off the hand throttle (i.e. push the lever all the way down), the throttle may still not have any effect on braking distance because: 1) If I have the clutch in (a common stick-shift driver reaction in an emergency), the throttle position doesn't matter for braking. It might "race the engine" more, but that would be it. and 2) And if I brake very fast "in gear" without pushing in the clutch, I'll likely "kill the engine" anyway. And throttle position also doesn't affect braking after the engine dies!