There are tons of digital camcorders to choose from.

Personally, I like JVC, and Sony.   Both have a few models with infrared taping capabilities...which mean you can tape with little or low light.  

In terms of the budget, I think you may have to up the ante by a few $$$ to get this feature.

Take a look at the Canon Optura and Elura models some of the best reasonably priced DV cameras on the market. Sony cameras are great also, I have used Sony cameras for years. Problem is that DV cameras start at $500 so you are starting with lowest model cameras. Digital makes it very easy to edit on a computer later. Another great alternative to DV is a new camera from Hitachi that records on a mini DVD in the camera it is very cool.You can then play back on your home DVD player. The Hitachi camera also has USB 2 for transfering files to a computer. These are $700-1200. Basically most of the cameras that you would want would be in that price range. My first consumer DV camera cost $4000.

Make sure the camera has a swing around LCD screen so you can see if you are in the picture. Get a tripod too.

Also do you only make love in the dark? Most pornos use lights you know... Or are you letting your partner know you are shooting? Anyway you should leave some lights on or the picture gets all grainy, They don't have to be really bright but all really low light shots look crappy in my opinion. Like night vision goggles.

be very careful about low-level performance. Not sure but DV might be poor at this. Possibly look for a camcorder that has a penchant for lowlight. I have a really nice Sony TRV900 which has a beautiful look in good light but gets very noisy even an hour before sunset This was $2k several years ago. Indoors, after dark, I really have to use hotlights. Even regular light fixtures don't cut the crappy picture.

I bought a Panasonic for under $500 through Costco.com 6 months ago and have been very happy with its low light peformance. Needs a fire wire port to download to PC, but also got a Pinnacle Studio editing software with FW board for ~$100 through Costco. Haven't tried taping sex yet, but was taped playing ice hockey, which is almost as much fun as sex!