I am in a similar situation. To be honest, the most painful part is thinking too much about it.
Just try to patch it up as much as it makes sense to (probably $ wise)
This is the approach I am taking...FYI HARBOR FREIGHT is your friend. I wish we had them in Canada!
1. Wire Brush / Wire Wheel the visible rust
2. Use a rust converter like Picklex 20, Rust Mort, or Osphos. I am going to try Picklex 20 as it's supposedly not as corrosive as others.
3. Then I will use something simple like Zero Rust paint or Rustoleum/Tremclad rust paint (oil based). Lots of people rave about POR-15, but there are stories on both sides of the fence.
4. Use Eastwood Internal Chassis Paint / Fluid Film on the internal frame
This will cost the most in time to do this, but material wise, I am estimating:
- Wire Wheel/Brush $5-20 from harbor freight. I got a nyalox brush (grey 80 grit), and some metal ones.
- Drill / Grinder (depends on the wire wheel/brush you choose)
- cheap/acid paint brushes
- Picklex 20 - pint = $50 ...i chose this as it sounds the easiest/minimal prep work. (Rust mort or other phospheric acid solutions are cheaper)
- Rustoleum/Tremclad = $20-30 per gallon, or Zero Rust $80-100? per gallon. Or you can get aerosol cans if thats easier. The key thing is the rust converter that will be what you will paint on top of. Others also suggest a primer on top of this, but i am not sure if i will be doing this
- Eastwood Internal Frame Chassis sprays (3 bottles, about $20 a piece)
For maintenance if you live in salted area, it might be best to get some gallons/cans of fluid film (in bulk-$10/can) to do an annual fluid film job on the underside.
Good luck sir. May your noble steed live long and prosper!