From what I hear, the 50D is a good reg. $150-$200 for a package consisting of a used reg (+ octo?) and a used dive computer (working?) sounds like an excellent deal. But there are a lot of good deals out there if one is patient.
With regard to the computer...
The Oceanic Datamax Pro Plus computer is an air-integrated nitrox-capable computer. I'd ask whether it works properly (accurate depth reading, accurate tank psi reading, etc.). You should know that this computer uses a Tadiran TL-2150 battery which costs about $6-$7 online. It is user-replaceable.
With regard to the reg...
Before buying anything, I'd inquire about the date of the last reg servicing, when it was last used on a dive, how it was stored since then, and the current specs of the reg (i.p. being delivered by first stage, cracking pressure of any second stages connected to it). I'd also ask about the overall cosmetic appearance of the reg setup (if that's important to you). I would then verify these things in person if at all possible. If the reg requires any servicing at all, as purchaser of a second-hand item, you'd be on the hook for those fees (labor + parts). How much does such repair work cost? Do your research on this. It can run anywhere from $50-$200 for a used reg setup (two 2nd stages and one 1st stage).
If you have the time, patience, and enthusiasm to learn how to DIY service the reg, purchasing a used one in good condition can make a lot of economic sense. I overhaul my own Apeks regs, and it's a fairly straightforward process. The design of Zeagle regs is very similar, so I'd think that working on them would be rather straightforward, too.
If you plan on having a local reg tech overhaul the reg for you as needed (when the reg actually requires servicing as indicated by periodic checks), buying a used reg can also be a good deal since lots of regs with the proper maintenance can go 2+ years in-between overhauls.
You should know that Zeagle provides a free-overhaul-parts-for-life policy for new regs purchased from an authorized dealer as long as that reg is overhauled once every year...but the new reg owner must still pay labor costs on that servicing ($50-$80 for a typical reg setup consisting of two 2nd stages + one 1st stage).
FYI, ZeagleExpress.com sells official Zeagle reg overhaul kits for a reasonable price ($25.30 for 1st stage kit, $16 for 2nd stage kit).
Take all of the above info into consideration before deciding to make the purchase. One nice thing about buying a new reg from an authorized dealer is that you are guaranteed to have a working reg for at least a year or two (probably longer with the right maintenance). If the reg has any issues, you simply take the reg back to where you bought it and say, "Please fix it."
For people considering buying used regs, I usually recommend that they check out the cost of buying a new reg at Scubatoys.com. Scubatoys is an authorized dealer for all of the gear it sells. The company has excellent prices and wonderful customer service. Scubatoys also does mail-order reg servicing for a very fair price. Turn-around time on reg servicing is surprisingly quick.