has to happen some time.

1. blu is one of the originals - from when street art went 2.0 (and blew up via the internet, primarily on wooster collective in the early 2000s).
(a) his peers are Banksy, Os Gemeos, JR, Swoon, Shepherd Fairey
(*) they were all featured in ART IN THE STREETS at MoCA (LA), though Blu's mural was censored before the exhibit opened
(**) blu, JR & Os Gemeos were also featured in Street Art at Tate Modern
(***) banksy famously painted the west bank barrier wall & in 2007 invited blu & Swoon to put up work on that wall (part of santa's ghetto 2007) & JR also 
(****) blu's street painting based animations (muto & big bang big boom) are singular and sublime, whimsical and telling, insightful, politically engaged
(b) the above listed peers have all been expanding their practices since the 2000s, producing a lot of collectible works (and also public works)
(c) blu has been expanding his mural practice across that time frame as well (blublu.org/b/walls/), making many building-sized politically engaged murals (but creating no works for the market - nothing for sale since 2012). as detailed in his recent book of 15 years of building sized murals (blublu.org/b/2018/02/21/minima-muralia-out-now/) and highlighted (thisiscolossal.com)

2. blu's work is extremely rare
(a) across his career he made less than 2000 editioned prints (in total, counting every screen print from every edition, and the etchings).
(b) small drawings, and a handful of large drawings, from his sketchbooks are his only originals released to market
(c) he has released 0 collectible works (editioned prints or drawings) over the past 8 years

in fact, that rate still feels like a bargain to me given his significance (and in contrast to the market success of his peers).

Blu should be seen almost like banksy, if the world was fair.

BLU is an hardcore 100% street artist who doesn't give a F*** about collectors and art market.

with all artist looking for fame and money he care only about his ART that makes him a REAL artist.

One of a kind he really is an outstanding artist totally undervalued.

and yes he is ITALIAN

So before all you speculators get all excited that Blu will be the (next get rich quick) Banksy hold your horses. The limited nature of Blu's sellable art is exactly why it will never be worth big money. Art markets are driven by those who have financial interests. There just isn't enough money to be made for the market to be propped up as is required to achieve crazy prices. So just walk away and leave the Blu stuff those who are quite content to enjoy his work knowing it will never make great investments.

Il nulla is the worst print imho.

I definitely love Blu's print, all of them, Il Nulla as well. 3k is definitely a huge amount of money but at the end he is not so "famous" yet, and once some galleries will decide to push him into the market we will look back saying "damn 3k, why I didn't buy it!"
It's out of my hands but if I could afford it I would enjoy it on my wall and it could be a good investment.