I would encourage you not to worry about cost. The expensive part of the journey up to Jungfraujoch is from Eigergletscher station (the farthest up you can hike) to the top and back. Travel below that is much less expensive.
The transportation in the Jungfrau region is managed by the Jungfraubahn. You can research all the fares for mountain transports (trains, gondolas, cable cars, etc at http://www.jungfrau.ch/en/desktopdefault.aspx/tabid-4//327_read-2542/
You are wise to understand that weather is a consideration! You don't say when you are going but you should always dress in layers, have a waterproof shell, and sunblock.
Specific answers to your query:
[1. Cable car Lauterbrunnen to Mannlichen, hike to Kleine Scheidegg, ride to Jungfraujoch, ride back to KS, hike down to Wengen, cable car to Lauterbrunnen?]
There is no cable car from Lauterbrunnen to Mannlichen. You must take the train from Lauterbrunnen to Wengen, then the gondola from the center of Wengen up to Mannlichen. Both are very lovely rides. The train is 15 – 20 minutes, the gondola 7 minutes.
The hike from Mannlichen to Kleine Scheidegg is stunning and a “must do” (by the way, walking is the only way you can get between these two points). It is about 2.8 miles on a very wide path with 50 meters/160 feet ascent and 200 meters /660 feet of gradual descent. A very easy hike but extremely panoramic.
From Kleine Scheidegg you could either take the train up to Jungfraujoch or hike up to Eigergletscher station and catch the Jungfraujoch train on its way up there. The hike up is short (less than a mile) but a little bit steep with 260 meters/858 feet of vertical ascent. It is a 10 minute train ride between Kleine Scheidegg and Eigergletscher station.
On your return, you could certainly hike down from Kleine Scheidegg to Wengen. It is about 4 miles, 785 meters/2600 feet of descent, takes about 2 hours. You would then take the train (no cable car) from Wengen down to Lauterbrunnen.
[2. Cable car to Jungfraujoch, ride back to KS, hike down to Wengen, cable car to Lauterbrunnen?]
There is no cable car to Jungfaujoch, only train. You could go directly up from Lauterbrunnen to Jungfraujoch by train. You will stop (but not change trains) in Wengen, stop and change trains in Kleine Scheidegg, then go straight up from there with a stop (no train change) at Eigergletscher station.
[3. Hiking from Lauterbrunnen to Wengen, then to KS. roundtrip to Jungfraujoch, hike down from KS to Lauterbrunnen or hike down from KS to Wengen, cable car to Lauterbrunnen.]
Hiking from Lauterbrunnen to Kleine Scheidegg (via Wengen) is probably a bit more than you will want to do. The Wengen to KS portion alone is 4 miles with 785 meters/2600 feet of ascent. The hike from Lauterbrunnen to Wengen is steep in places and is about the same amount of distance and climbing. That would be a long hike!
My recommendation would be to take the train from Lauterbrunnen to Wengen, the gondola from Wengen to Mannlichen, hike from Mannlichen to Kleine Scheidegg, take the train up to Jungfraujoch, return by train to Kleine Scheidegg, hike from Kleine Scheidegg to Wengen, then take the train back down to Lauterbrunnen. This is the best from a difficulty and views standpoint.
There are very good descriptions of hikes in the area (including some of these) at www.walkingswitzerland.com