What is the difference between USD 38M and USD 120M CGI?

As with many things in life, if you can spend more money on something, you can usually expect a higher caliber of quality.

The budget for Riddick was mainly comprised of funding that Vin Diesel raised himself. He mortgaged his house, took out loans, and spent his own financial reserves for the film to even see the light of day. He was literally quoted as saying if they couldn't finish the film, he'd be homeless.

The likely reason it was hard to come up with funding is because the previous film in the series, The Chronicles of Riddick, was considered to be a financial flop. With a reported budget of between $105 million and $120 million (remember: those figures do not include marketing and distribution costs), Chronicles only grossed around $115 million, and only $57 million of that was domestic.

I mean it's quite simple really. You can't expect special effects on the level of, say, Avatar, when your budget isn't even 20% of Avatar's budget. In the case of Riddick, its budget was merely 32% of the total budget for the previous film. Less money to spend means you have to reign in on things like special effects and CGI. You can't afford the best, and you can't afford a large team of special effects and CGI artists.

Less budget means less time to let people work on stuff. CGI isn't only about rendering time. In order to have good CGI you need models, which are made by artist. There's not much that has changed in this process of creating models and textures compared to 2004; you still have to come up with all the details and animations yourself. Furthermore, most of this stuff is made by "hand" (using computers).

Everyone has to get paid for their job, so if you have less to pay, you cannot afford the same amount of details and creativity.

That being said, of course some steps of the CGI chain cost less nowadays. Such as rendering due to faster computers and newer techniques. But still there's a creative process attached to CGI that is done by humans, that in the end, want to get paid for their work.

This question asks for things that are primarily opinion-based and that can't be baked by a good quality of sources and so is this answer.

Doing (and financing / budgeting) CGI scenes and animation in movie is pretty much similar than doing a computer game with 3D graphics or animation.

Key elements that influences budget:

• number of worlds or locations (different objects, NPCs, lighthing, physics?),
• number of characters (abilities, interactions),
• number of vehicles, devices, artefacts etc.

In addition for movie (and for cut-scenes in games):

• number of real actors that interacts with CGI.

In Riddick (2013):

• there is only one world (deserted planet) + Necromongers ship in some cameos,
• there are no space rides and fights, no chases with CGI,
• number of characters is limited to 9-10 and all of them are human,
• no character has any abilities that would require intense CGI,
• there is very little interaction between a living actor and CGI creature,
• there are only two ships and they only land, there are no pure CGI devices or artifacts,
• number of wide scenes is very limited,
• the "planets popping from water" devices is most likely rendered again, but I am sure that using "old" models from previous movie.

In Chronicles of Riddick (2004):

• there are a lot of worlds (Helion Prime / New Mekka, Crematoria, frozen planet etc.),
• there are quite a few scenes with Necromonger's armada, space attacks, in-flight fights etc.,
• there is a jail ride and frozen planet chase,
• there are a lot of characters, quite a few battle scenes, arena fight etc.,
• there's a Lord Marshal that has his soul-like intense CGI ability and a lot of interaction between this character and living actor,
• there are a lot of ships, other types of vehicles and artefacts,
• there are quite a few wide scenes (Necromongers attack, armada leave),
• there is a number of wide scenes that requires intense CGI in addition to actor's play (frozen planet, burned down Crematoria surface etc.).

These are only few examples. In general, number of locations, characters and their abilities requiring intense CGI, vehicles, devices, artefacts, scenes and creatures is by far bigger in Chronicles of Riddick (2004) than in Riddick (2013).