Using 100 ME: You get around 2k for doing the first two levels. If you use all your energy, you end up with 10k. Buy 100 CE. Use that to get 100 more CE. Rinse and repeat.
You get 1kcr profit every 100 energy. (Today's Economy: 9kcr->100ce)
Each run takes about 30 minutes, so you can get 2kcr in an hour. Assuming you play 4 hours a day, you can get 8kcr a day.

Assuming you're starting from scratch, let's say from 2*, you will have to buy the 2* recipe (1,000cr), craft it (50ce + 400cr-> 4,400cr), buy the 3* recipe (4,000cr), craft it (200ce+1,000cr->18,000cr), buy the 4* recipe (10,000cr), craft it (400ce+2,500cr->37,500cr), and then finally buy the 5* recipe (25,000cr), and craft it (800ce+5,000cr->73,000cr), which totals up to: 172,900cr. That is roughly 21 days of playing the first two levels of RJP every day for 4 hours a day.

Did you only mean 5*?
Thatis 25,000cr for the recipe and 73,000cr for the crafting, so around 98,000cr. 12 days of 4hour farming.

What I would suggest is you start farming IMF tokens. The twins are relatively easy. You lose your profit by doing the boss, but you get 3 tokens every 30 minutes. You need 15 to buy a pulsar. If you save up for an unbind for the pulsar (200ce->18,000cr, which is one or two days of heavy RJP farming), unbind one, and sell it on the AH for around 30kcr, you get 12,000cr profit, which took two hours and a half. Which is around 5kcr an hour. 20kcr a day. That beats RJP farming by 12k a day. Instead of 21 days, that's 5 days.

But WAIT, there's more!

You can also do the same for RJP tokens, buy a sealed sword, unbind, and sell. You get about the same amount of profit, but this is riskier and harder. Only recommended once you get a Dark Retribution or something like that. Also note that Sealed Swords cost 20 tokens, not 15.

There's EVEN MORE!
You can do this with Vanaduke as well, once you unlock him. There is a MUCH higher risk/reward, but if it works out for you, great. If it doesn't, I warned you. You can buy Blackened Crests, unbind for 1,800 CE (162,000cr) and sell for 225kcr or more. That's a huge profit, but you need to watch the AH closely to see if others are doing this as well, and how successful it is at the time you want to sell it. Blackened Crests: 30 tokens.

I'm sorry. I rambled. But, that's how long it will take: 21 days. As I said previously, I suggest farming pulsars, or if you think it's too hard to, get into a noob-friendly guild that will invite you along some FSC runs. They both give roughly the same amount of crowns, with FSC being the safer, more economically-challenged-friendly, and the IMF being the more skillfully-challenged-friendly.

There's more risk in unbinding, but if you can pull it off, you can start to make big money.

Honestly, buying CE to run levels other than FSC is a terrible waste of time (unless you also want to have the fun of playing that particular level at that particular time, in which case, great). 2kcr an hour? Ugh, why bother? You could make far more sitting at the AH, buying cheap 2*s when they end at auction, and putting them up again for realistic BINs. I made over 10kcr a day doing this as a noob (scaling up as I made more), and it sure didn't take me anywhere near 4h.

I assumed that he wanted information around making money from boss runs... But yeah, there are better ways to make money.