If you can't afford to do it correctly now, then wait until you can. There's no point in putting the car up on jackstands and leveling it twice, plus tearing out carpet and other materials that are in the way twice. Then there's dragging the welder out twice and scheduling a pro welder twice if you're not reaaaaaal good with a welder.

Just wait 'til you can do it all at once and do it right. The main hoop by itself won't stiffen the car appreciably.