I'm with Peddler. If you are going to do it - do it properly. There's a saying about helmets - buy a fifty dollar helmet for a fifty dollar head. And the same applies to any safety gear - get the best you can afford. Even if it is 'just' for Hillclimbs and sprints - I've seen some very big accidents and rollovers at both.
$800 is dirt cheap for an approved cage, but I wouldn't expect it to be anything more than the absolute minimum bare bones 6 point job. Ensure it complys with CAMS drawings, and it's concerning to hear that some might not come with any diagonal member. They are mandatory.
If you are building a race car in particular, I'd get the most comprehensive cage you can afford. Not only is it the only thing between you and every other idiot on the track, but it provides the basis of the chassis for the suspension to work off. I cannot believe the difference in the car since I got my cage! To give you an idea, most race-fab shops up here start prices from around $1800 or $2000 and go up from there depening on what you want. Be very careful when looking at cheaper alternatives, and make sure you know that section of the CAMS manual inside out before talking to the chaper cage builders. There are a few reputable cage builders around who are prepared to do the job for less if you hunt around long enough. I can recommend one in SEQ, but that doesn't really help you guys I guess. Having the cage built as opposed to an off the shelf bolt-in, allows you to tie the cage in to the bodyshell in alot more areas. Mine has something like 18 attachment points
front sectionrear section