April 10th is in 22 days!!!! By the time it arrives and you pull it from customs, it will take another 7-10 days...
If you wanna buy machines now, then lets say it's 4500$.
Shipping to my country is 800$ , taxes are 20%, customs, 2-5%.. Lets suppose value written on invoice is 2000$.. If you put less, you risk customs will confiscate it because they will check on ebay how much it costs...
Company that will do the customs duty papers and delivery is 100$ at least.. There are other smaller expenses, but let's say that's it.. We come to ~5900$ if you buy NOW...
If you will wait until april 10th, then price will of course be lower, but only for the amount of money you would earn by then..

As for difficulty, it will average to 20% IF bitcoin price jumps, I am sure of it.. Now, when it's worse then ever to make a ROI, diff increase is estimated at 12-14%... That's my opinion at least..

Ok, put the diff increase at 15%..
By calculations, machine of 1Th/s arrived at 29.03. at price 5900$(with shipping+customs+taxes included) will pay of exactly at new years eve
And assuming price of 636$ per BTC..

from AliExpress.com , ebay, amazon, http://bitmine.ch/?product=coincraft-rig-mid-january-batch

BTW, based on https://twitter.com/BITMAINtech
their s2 will cost 3900$ but ships on 10th of april... While my find(5900$) would be shipped on 20th of march...
Also, I said 6500$ is with all other expenses included!

So, if we say that 1Th/s machines now cost 5900$ plus shipping and optional customs/tax, let's say it's 6500$ in total...
If I enter into calculator that:
- average diff increase is 20%
- electricity bills are 0$
maximum profit this machine can make before new year is: 5400$

Now did I get something wrong or what?!?!
Check yourself:

http://aleks1k.github.io/bitcoin-calculator/?Hashrate=1&HashrateLevel=1e12&HardwarePower=200&Difficulty=4250217919.87&DifficultyIncrement=0.203&StartDate=NaN&EndDate=NaN&PoolFee=0&ElectricityPrice=0&Currency=USD&CurrencyRate=636.66#BTC