So rough estimates....

7 Sacreds, 30M silver, 1000 gems.  

Shards are always the most crucial but if youre doing UNM everyday you get plenty in-between fusions to do them all if you choose.

Since you are late game already, you can easily complete fusions with the resources the game provides.  

For many players, it does require a shift in play-style:  Shards, Soulstones & Gems are resources that must be saved and managed in order to facilitate the compeltion of Fusions, Titan Events & Path Events.

If you can't embrace that Deferal of Gratification, you won't be able to complete fusions and other events as a F2P player. 

Hydrid Fusions are the toughest; Traditional are the mid-ground; Frag collectors are the easiest. The fusion that starts next week is a frag collector, so that is the best time to get your feet wet....assuming you have some Sacreds in the bank.

@DarkM00se 

I am doing this Summon Rush the grindy way because I do not want to pull Sacreds.  I have every one of the non-void burners that are on boost, and I came out of the Leo Path Event 12 into Mercy, so I really don't want to burn my Mercy on this.  

I had a lot of campaign to catch up on for my Monthly 500, so I am doing about 400 campaign battles to earn Diver Points and Mystery Shards.

I'll grab the first 5 Kroz Frags for 850 Greens and a 10-Pack of Voids.  I already have Venus & Sulfuryion, so I'll probably boost Supreme Galek.  

Anyway, this ramble was to demonstrate how to do an SR on the cheap.

I went a bit more expensive but 3 Sacreds + 4 Voids isnt a terrible ROI. 

@DarkM00se 

Were you able to complete the Kroz fragment event?  If so, you now have a feel for the resources required.  

A frag collector like Kroz is the easiest type of fusion.  The Yukimasa fusion starting on Monday will be a traditional fusion, which is the middle ground in terms of time/resources required.  Yukimasa definitely looks like a fusion worth doing.        

100%.  Very good for both PvE and PvP.