realistically you're looking at [CLAIM,CLAIM,MOVE,MOVE] or you will be stuck at 1 / 5000 reservation points and every time your reservation creep gets replaced the energy source will drop back down to 1500 losing you precious energy.
So yes, it is costly to reserve a room. You are effectively spending between 2600 to 3900 ( 2 or 3 reservation creeps) per 1500 ticks to hold your reservation. Assuming you are spending 100 ticks just traveling to the controller, you still earn 800 reservation per creep, giving you effectively 2400 / 5000 reservation in the first 1500 ticks.
As for profit, you have just spend 3900 on claims. Assume you spend another 2100 for miners and haulers, and you are looking at around 9000 net profit per 1500 ticks. This increases further after the first two cycles because it is not necessary to continue to dump 3 reservation creeps in every 1500 to maintain your reservation at max level (5000/5000). so that drops off to 2600 and 2100 giving you over 10,000 in profit from a single source.
I would say 10,000 is preferable to the 7500 you could get not bothering with the claim, but it does take a bit more work to set up. It is well worth doing for any two source rooms you have nearby.