Rust covered and rusted through are two different things. If it is rust covered remove the rust paint it and go. That is what I think most normal folks do. HOWEVER.... If you can not clean or repair it to a functional state. you can buy a fabricated one for a ton of cash or you could look for a nova or s10 which may also be rust covered. You may even be able to locate a frame that from an identical truck for very cheap if the rest of the truck is trashed. <---would prevent some fabrications with fitting it all back together later.
Good luck

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