Those were superb dive timers, but they were not computers as they only provided depth, max depth, temp and dive time. Beuchat marketed them as basically a digital depth gauge and dive timer and we found them to be very useful for students as they did not have to worry about tracking start and end times on the dive - something many of them forgot to do otherwise.
The dive timer you have is in fact the original Uwatec bottom timer - the same thing marketed later by Uwatec/Scubapro. The first Uwatec/Scubapro version was identical to the one you have except for the mostly blue cosmetics and branding. The current Uwatec/Scubapro version has a redesigned cosmetic treatment and deeper depth rating and a longer battery life, but retains the same screen, layout and construction. OMS also marketed the same bottom timer with it's own mostly black cosmetic treatment, but it was again the same bottom timer made on the same production line. Consequently all of them, from the earliest to the present, are sealed units. Back in the day there was a guy cracking them open and doing battery replacements, but as I recall the results were mixed, and I doubt he is still doing it.
Your best low cost air only diving option is to look for one of the older Oceanic hockey puck computers on E-bay, such as the US Divers Matrix or Matrix Master, or the Oceanic Datamax, Data 100 or Prodigy. They are air only rather than nitrox computers, but they usually sell for less than $100, they use a pair of readily available 2032 batteries, they pretty much last forever, and like the Uwatec bottom timers, they fit the depth gauge spot on a standard console.
Oceanic also made the DataMax II which was a regular depth gauge with an integrated digital bottom time. Those show up now and then in working condition and usually they sell for well under $50 as there is no deco information provided. Dacor had something similar but I don't remember what they called it.
