Gear upgrade costs from +0 to +20, what spare gear returns, and where Memorium comes from.
What upgrading does
Upgrading raises stats. +5, +10, +15 and +20 each unlock a substat (up to four) or upgrade one.
Rarity sets the starting substats. Stars set stat size, so higher-star pieces stay stronger.
Upgrades cost Gold and Memorium.
Rarity
Substats at +0
Common
0
Uncommon
1
Rare
2
Epic
3
Legendary
4
Upgrade cost
Totals for each block of five levels.
6★ gear by rarity
Rarity
+0 → +5
+5 → +10
+10 → +15
+15 → +20
Gold to +20
Memorium to +20
Common
9,540
51,440
253,050
1,285,970
1,600,000
6,600
Uncommon
9,920
53,500
263,160
1,337,410
1,663,990
6,600
Rare
10,720
57,770
284,220
1,444,400
1,797,110
6,600
Epic
12,000
64,700
318,330
1,617,730
2,012,760
6,600
Legendary
13,920
75,060
369,270
1,876,580
2,334,830
6,600
Greater
19,210
103,590
509,590
2,589,670
3,222,060
6,600
Memorium, any rarity
300
739
2,385
3,176
–
6,600
Legendary gear by stars
Stars
+0 → +5
+5 → +10
+10 → +15
+15 → +20
Gold to +20
Memorium to +20
1★
3,040
16,430
80,770
410,510
510,750
200
2★
4,360
23,460
115,390
586,430
729,640
400
3★
6,530
35,190
173,090
879,640
1,094,450
700
4★
7,820
42,230
207,710
1,055,570
1,313,330
1,650
5★
10,010
53,940
265,400
1,348,790
1,678,140
3,520
6★
13,920
75,060
369,270
1,876,580
2,334,830
6,600
About 80% of the gold goes on +15 to +20. +15 costs under a fifth of the full price, so push to +20 only on pieces you'll keep.
Rarity barely changes the price. A 6★ Legendary costs 1.46 times a 6★ Common to max, and the Memorium is the same for every rarity.
Stars change it a lot. A 6★ piece takes 33 times the Memorium of a 1★ piece, against 4.6 times the gold.
Accessories cost the same as gear of the same stars and rarity.
Cost per level
To level
Gold
Memorium
Gold from +0
Memorium from +0
Selling, deactivating and destroying
Spare gear can be sold or deactivated for Gold, or destroyed for Memorium to fund your best pieces. Base returns by stars and rarity are below. A 6★ Legendary sells for 138,000 Gold.
Sell for Gold
Stars
Common
Uncommon
Rare
Epic
Legendary
Greater
1★
1,000
1,050
1,100
1,140
1,190
–
2★
1,500
1,560
1,620
1,680
1,750
–
3★
2,000
2,100
2,200
2,300
2,400
–
4★
10,000
10,400
10,800
11,200
11,600
–
5★
25,000
28,000
31,000
47,000
71,000
–
6★
50,000
55,000
61,000
92,000
138,000
207,000
Deactivate for Gold
Stars
Common
Uncommon
Rare
Epic
Legendary
Greater
1★
500
520
540
560
580
–
2★
1,000
1,040
1,080
1,120
1,160
–
3★
2,000
2,100
2,200
2,300
2,400
–
4★
10,000
10,400
10,800
11,200
11,600
–
5★
40,000
42,000
44,000
46,000
48,000
–
6★
60,000
62,000
64,000
67,000
70,000
81,000
Destroy for Memorium
Stars
Memorium, any rarity
1★
5
2★
18
3★
48
4★
75
5★
125
6★
250
Accessories sell for the same as gear. Greater pieces are 6★ only.
Where Memorium comes from
Memorium is only used to upgrade gear. You get it from:
Campaign battles. Memorium drops from Campaign fights.
Spires. Clearing Spire floors gives Memorium among the rewards.
Destroying gear you don't need, as above.
VIP. The VIP bonus multiplies the Memorium you win from battles.
The best stages per Energy, Spire floor rewards and Memorium packs: Where to farm Memorium.
Gold and 
Memorium.