If you are only going for the evening and not as part of a longer park-hopper stay, you might consider buying a partial ticket off eBay. Of course, the usual caution should be applied here and ALWAYS read the auction carefully so you understand what you are buying. I have watched a couple of folks run a successful business of selling partial tickets on eBay (all vicariously, just seen them on eBay over time).
If you are going for the "first night" of a longer park-hopper ticket, that depends on how long your ticket is for. The more days on your hopper, the cheaper they are. If it's an extra $20 for one more day, that would be like a reduced price on the first evening.
I recently went over and scouted the area out before our Dec trip. I had one evening in LA on a business trip, so I headed over to DTD, ate, shopped and got the lay of the land. It was a little Disney, but it was free (don't stay too long or you'll have to pay for parking).