Straight vs. angled aircraft carrier decks: tradeoffs for rolling takeoff?
Correct, at the weights and speeds of most carrier based jets they would need several lengths of an aircraft carrier to get airborne.  Catapults became required as the airwings transferred to jets in the 1950s and 1960s.
Aircraft are stored in the hangar below decks, and on the sides.  Anywhere there is free space.  Even during simultaneous launch and recovery.  Look at photos and videos, it can get crowded!
Since we aren't building straight deck and angle deck carriers that are otherwise similar, a fair cost comparison cannot really be made.  (Amphibious ships serving VTOL aircraft lack catapults and arresting gear which would account somewhat for their lower cost.)  Propulsion, radar systems, inflation, and many other factors also account for the increased cost of modern carriers over earlier straight deck ships.  And it is not true that you need a nuclear reactor to generate steam for the catapults.  Steam catapults were around for quite some time before the first nuke boat. 


ADDENDUM:   There isn’t enough space in the comments section to refute the multiple inaccuracies in Peter Smith’s response to this question, so I will address them here:  

All modern US Navy carriers have 4 catapults, 2 at the bow and 2 at the waist.  (This has been consistent for the last 40-50 years)  The “waist” catapults (cats 3 &amp; 4) are so named because they are amidships, and thus cannot be used during landing operations because they foul the landing area.  The photo in his answer shows the two bow catapults.  The one pictured on the right is NOT a waist catapult, it is cat 1.

Simultaneous launch and recovery is possible however.  Generally the launch starts first while the previous cycle is holding overhead, using all 4 catapults for efficiency.  Once they get to a point where most of the next cycle is airborne and the landing area is clear, they will “wrap” the waist catapults and begin recovering the earlier cycle while they finish launching off the bow.  

The only caveat is that longer wingspan aircraft like the Tomcat and E2 will foul the landing area if they are on the left bow catapult (cat 2) with their wings spread.  For this reason they will finish launching them from the right bow catapult (cat 1) if recoveries have begun.  This is not a problem with Hornets, and possibly not an issue on the largest of carriers. 

There is almost always some overlap where simultaneous launch and recovery occurs during normal cyclic operations.  And during pilot qual/requal, the deck runs continuously.  You will land, fold your wings, taxi to the bow cat, spread your wings and launch again...  It is a continuous stream of simultaneous launch and recovery operations.  

It is also definitely not true that aircraft are not parked anywhere but the bow during recovery.  Any spot outside the landing area foul lines is fair game.  It is a very common sight to see aircraft parked on both sides of the landing area on final approach.  But don’t take my word for it, there are lots of videos and photos on line to verify this…

Finally, the arresting cables are not forward of the “aft lift” you show in your photo.  (Elevator 1 or JBD?)  Again, this photo is of the bow only.  The two waist catapults and the landing area are well aft and left of the perspective this photo was taken from.   

BTW, the diagram of the angle deck carrier in the question is not an accurate representation of the current class of US Navy fixed wing CVN Carriers.  Below is a good diagram showing the layout of the 4 catapults in relationship to the landing area.