I was looking for that quote (i.e. average costs go up by 1 cent), but I couldn't find it. It wasn't in the company press release. I found this, though, from Forbes: "According to Neeleman, regional flights on the Embraers would cost about one cent more per passenger-mile than the longer routes, so JetBlue will charge higher prices than it now does." That doesn't sound like average costs to me.
I did find another quote that mentioned that the EMB-190 would only cost $6 more per seat than the A-320 to make a 600 mile trip. Now, it's not very straightforward to make an apples to apples comparison with just that information, but you can make some analysis from other existing data.
For the 1st quarter, system CASM was 6.25 cents and the average stage length was 1169. So the average trip cost was 1169 * 162 * .0625 = $11836. A 600 mile trip is about 51% of that length, so the cost would be less, but still more than 51% as much due to fixed costs. Call it 70% to be conservative. So, a 600 mile trip in the A-320 would cost $8285. Dividing back out, the CASM for a 600 mile trip is 8.52 cents. The cost per seat is $51.14.
If the cost per seat in the EMB-190 is $6 more on a 600 mile trip, then that cost would be $57.14. Its CASM would therefore come out to 9.52 cents, exactly one cent more than the A-320's, not 4 cents more. The math does work, and it is consistent with what we know about JetBlue's current operating costs.
JetBlue employs an analyst staff that crunches numbers on everything (potential routes, costs, traffic, yields, etc.), and they are very conservative. They like to beat estimates, and don't like to be overly optimistic. If they think that costs on the -190 will only be a cent higher on medium-short routes than on the -320, you can assume that it will be pretty close to that. They have proven to be frighteningly prescient, and I'm inclined to believe them on this.
Timz, if the BELF on the -190 is expected to be 60%, as opposed to 70% or so on the -320 (it was 70.8% in 1Q), that reflects a higher expected RASM on the -190 routes, since those routes will be planned to avoid LCC competition. The math works here, too. If a 600 mile trip costs $5714, and the load factor is 60%, you would need an average fare of only $95.23 to break even. With the right route selection, that should be easily sustainable. You'd only need an average fare of $114.32 to make a 20% operating profit, which is phenomenal.