This year buying an Esrog is different then other years because of shemitta. Shemitta raises a number of different problems. Esrogim according to the consensus of poskim have קדושת שביעית. Here are some of the issues:
1. שמור - shemitta fruits need to be made hefker, if they are not they may be assur and may not be able to be used for the mitzva
2. נעבד - you are not allowed to do various melachos related to the esrog tree during שמיטה. Again if these are done the esrog may not be able to be used for the mitzva
3. סחורה - you are not allowed to buy/sell shemitta produce.
To get around all of these issues many people are buying אוצר בית דין esrogim. The אוצר בית דין watched the orchards and made sure that there was no forbidden melacha going on. they also were מפקיר כדין. The esrogim are also sold in sealed boxes so you can't go and pick out a specific esrog.
The big issue is what about סחורה? The answer is that the אוצר בית דין is allowed to charge in order to cover their costs. Therefore when you buy an אוצר בית דין esrog, all you are paying for is the actual cost in producing the esrog, there is no profit to anyone.
There is 1 major problem. All of the אוצר בית דין are selling esrogim in 3 different price ranges:
1. כשר - these sell for 40-60 shekel depending on the אוצר בית דין
2. mehudar - these sell for 80-100 shekel depending on the אוצר בית דין
3. mehudar א - these sell for 130-150 shekel depending on the אוצר בית דין
If as we said all the אוצר בית דין is doing is recovering costs, how can they charge more for a better esrog? The answer given is as follows.
The אוצר בית דין has for arguments sake 1000 esrogim and needs to get back 75,000 shekel for their costs. If they tried to sell every esrog for 75 shekel people would not want to buy, there are always people who want a more mehudar esrog and are willing to pay more and there other people who can't afford to pay 75 shekel for an esrog. Therefore what the אוצר בית דין does is split the cost differently. They still get back only the 75,000 shekel however, the more mehudar esrogim subsidize the less mehudar ones. This enables them to sell the esrogim and get their costs back while enabling the more affluent buyer to spend a little more and the poorer buyer to spend a little less. Since no one is actually picking a specific esrog, you just get a sealed box, it still doesn't look like סחורה.
By the way, I bought 3 sealed אוצר בית דין esrogim this year and ended up with 3 beautiful esrogim that in a regular year I probably could not get.