hi friend ... all kidding aside, i would very seriously consider simply using a watch as your timer and an spg for your gas. first of all, you will most likely use them for the rest of your dive life as a backup to whatever computer you eventually do purchase. second, it will shape your use of tables (or electronic rdp) which you will also possible make use of in future dive plans. 3rd, i falls well within your price range.
a second choice and still quite a good one, is picking up a citizen dive watch which also give depth, temperatures (less important), and logs dives. you can get into a used one for around $125 most likely.
i think you may be looking for an unreasonable deal for $50 otherwise.
where are you located btw
also, where are you vacationing?
do you own the rest of your gear? honestly, a computer is not my first choice in 1st purchases. why would you want to use the gear at the place you will be? (dont get me wrong, i prefer my own gear as well, but if $ is holding you back, renting is fine). on top of that, if i needed to buy my own gear, i would certainly want regs first as they are actually in my mouth. there are many terrific deals on regs currently both used and new.... that being said, if you already have the rest of your gear, id seriously consider an spg and watch as a bottom timer.
not to insult your intellect but in case any of that was over your head, feel free to throw more questions out....
for example, spg stand for submersible pressure gauge
hope this was the least bit helpful
