I have a 1998 Chevy Blazer LT all 3 O2 sensors are tripping which failed my inspection the truck doesn't bog, no long start does seem like gas mileage is a bit low other than that the cat converter rattles like crazy need this thing to pass soon help

 

All signs point to you needing a replacement cat. Is the cat itself rattling, or is it the heat shield? I'm having mine replaced this weekend, and the local shop is charging about $200 (thats part and labor) to replace it. That should give you an estimate on what you may be looking to spend, but if your cat itself is rattling (not the heat shield), you'll definitely want to replace it.

 

Had my Cat done on my old 97, and it was like $250 for parts and labor, in MN. That price sounds about right. Now as to why it's triggering all 3 sensors is odd. If anything it should only trigger the 3rd, correct? Feel free to correct me if I'm wrong about that.

 

My cat triggered my bank 1, sensor 1 on its way out. After replacing both before-cat sensors, only then did it reveal a catalyst issue.

I would start by replacing all the O2 sensors. Its recommended that you do this when replacing the cat anyway; if you have a similar situation to mine, then the new sensors could likely trip a new CEL code identifying a catalyst issue. If the problem is the O2 sensors themselves, then you could come out cheaper.