Help me pick a trip computer + a question about gas miles per tank bar

[gabriel2012]

Hey guys first of all I would like to know if there are cheaper options to the scan guage 2 that work with the 2007 yaris hatch.

second and randomly, how many miles do you get for each bar of gas on the guage? I get around 42 avrg and mines an automatic. (my driving habbits are mostly city here in Puerto Rico, no more than 60mph and I always start off smoothly after a stop, using mobil1 5w-20 synth with mobil1 filter and the weather is mostly hot so the a/c is on most of the time on 3 and sometimes 2 when it gets to a decent temp, replaced airfilter recently aswell)
the last time I calculated my MPG was when I got the car around 3 years ago and I really don't remember so I'll start to count the next time I fill up.