A quick thought, I'm sure others will be seconding this remark...
I may join a gym eventually after I shed a few pounds to begin with weights but my main focus is really getting a cardio workout.
The best way for you to lose the weight is a combination of cardio and weight training and maybe even in the opposite order, weight training and cardio. I am currently doing the same thing and have found that advice through other threads over and over and over and over again within this forum.
Now, to your actual question...
Purchasing on the internet can definitely save you quite a bit of money. My only advice is to be sure you test the actual machine you want to buy in a store somewhere if at all possible before you buy. My wife and I bought an elliptical a few weeks ago and spent quite a long time trying different manufacturers and models before settling on the best one for us. Even if you've tried a Proform before, don't think another model will feel even remotely the same...they all differ.
For the most part the old saying is true...you get what you pay for. If you buy a cheap elliptical (I'd say $300 - $500) it will be low end and you should expect it to squeak a bit and not be extremely sturdy. This is not a bad thing if you can deal with it (especially if you are fairly light weight). Don't expect any elliptical to perform like one in a gym because those are extremely expensive and you probably don't want to sell your kidney or a child on the black market to get the money for it.
Another bit of advice...be sure to get a service plan. I haven't had to utilize ours yet (it's only been a few weeks), but everything I researched said you should definitely get one. The extra money will be well worth it two years down the road if/when something breaks.
Lastly, just to drive the point home,
don't buy before you try. They all feel different. Go to stores just to jump on and off different models if you haven't already just to prove this to yourself.
Just for the info...
We settled on the Nordic Track Audiostrider 800 from Sears. Got it for $699 with a three year extended service plan for an additional $129. We did get a little off of those prices ($30) by purchasing online and picking up instore.