There are several standard Deltas, and some special editions.
Basically, there were the original Deltas, which are in MKIV Series 80 configuration. They differ from a standard 1911 by having a commander style hammer with a round hole, and Colt's relieved grip safety. They have a dual recoil spring set up with a guide rod that has a buffer in it.
Then there are "Enhanced" Deltas. These have Gold Cup styled slanted cocking serrations, a flat top ribbed slide, a different roll mark, a frontstrap with an undercut under the trigger guard for a higher grip, a beavertail style grip safety, and a commander hammer with an oval hole.
The Delta Gold Cup is basically like the "Enhanced", but with a wider Gold Cup trigger, Gold Cup sear, and a Gold Cup rear sight.
I won't even get into the special editions.
The guide rod replacement is common because the original unit breaks under continous use. King's makes one of the better kits. However, many will go to an all steel guide rod, with a replacement spring. The dual factory springs are rated at 23 lbs., and most people I know run 24 lb. Wolff springs. I've run up to 26, but had functioning problems with those.
Price for a regular non Enhanced Delta would be around $700 for one in good condition, higher for a LNIB or NIB gun. I see them as low as $500 for beaters. Enhanced ones are a little bit more, and the Gold Cups are usually $1000 to $1200, depending on finish and condition.
Here are a couple Delta pics: