The rust in the pix doesn't look too bad. Poke it here & there w/ a sharp awl or a screwdriver to see how deep the rust goes.
Sandblasting is the fastest way to remove rust on the frame. Be sure to follow up w/ a good rust converter/acid etch to minimize future rust bleed-through.
For a short term fix, you may want to consider a "paint" product like Zero-Rust, Rust Encapsulator(from Eastwood), or POR-15. All of these products are designed to be applied directly to clean,grease free rust and do a good job until you have time to do it right. As far as which product works "best", I have used all 3 extensively and would recommend the Zero-Rust. It is the least expensive and works well.
