On page 160 in the magic item compendium ther is the everful mug 200gp 3 times a day will fill full of 12 ounces of cheap ale, water, or watery wine. Normally a human should consume roughly 4 liters (its rounded up) which is basically a gallon. theres a 128 fluid ounces in a gallon. In a desert environment you should drink 1.5 gallons roughly so roughly 192 fluid ounces and since everful mug only provides 36 ounces of water a day we will each need roughly 5 (6 if you round up because result of 192 divided by 36 is 5.3333333333333333333333.....). So thats a thousand gold in water (not including what personally i would have to pay for for the horse). then there's everlasting rations 350gp. Enough trail rations for a medium creature for 1 day it replenishes every day at dawn. For me and jenna i recommend we get 2-5 everlasting rations for us and the dragons that may hatch. And for my horse there is the everlasting feed bag is 800gp and it feeds the animal until taken off so ill probably need two to three. The horse will need to consume roughly 10 gallons of water a day that's 1280 fluid ounces a day so ill need 36 everful mugs for horse. So for normal character to survive desert just food and water wise they will need to spend 1,350 gp on food and water. Jenna would look more like 1,700 gp-2,750 gp. And i will need to spend between 12,300gp-13,350gp just in food and water. That's if we go by earth real world means. That's not including goggles, skin covers, security measures, things so we dont overheat, and any other things we may need to survive extreme heat(This is all for the get little miss dream souless her soul back).