Is it possible to do over a weekend? Yes. Is it likely to get it done cheap? Maybe. Is it an easy thing to do? No.
To do both sides of the frame is about an 8 hr job. That is if you have already prepped the area by pulling the fuel tank and getting all the bad sections cut out and removing the fuel lines and the electrical wires in the area to be welded. So figure an 8hr. job times what most professional welders get per hr. Which in this area is $80-$120/hr. So if you had it professionally done it would cost you between $640 and $960 for the pieces to be welded in.
To weld the repair parts onto the existing frame it has to be stitched together, because 1 continuous weld will create too much heat and the frame rails will warp. Thus the reason why it will take 8 hrs. to do the job.
You cant own a 20 something year old Jeep that needs repairs like yours without having all the tools to do the repairs needed, unless you have really deep pockets that are stuffed with boat loads of cash. Free or cheap just doesn't happen in the welding business, specially when it pertains to frame welding. Like it was said above, welding is an art, and if you want it done correctly, you will pay for the artist to do his work.
'87 YJ, 4.2L built and bored, 8.5" of lift, 8.8 rear, AX15/NP 231, Tom Woods drive shafts, Flat fenders, 12,000LB winch, Custom bumpers, Rattle can paint job. Never completed...