Poly-Vi-Sol made by Enfamil is less than $8 at Target. I looked at the Target store brand one since it is cheaper but the Target one did not have iron at all, so watch the labels if you go for one other than Enfamil. Otherwise you could try pediasure or a toddler formula, or buy the chewable kids vitamins and grind them up and add it to food. Also fortified cereals have plenty of vitamins and minerals and I try to make sure my 17 month old son gets cereal each morning [and for snacks] so that I don't worry so much. My son used to love multi-grain Cheerios [100% daily iron] and now he likes Corn Flakes [45% daily iron]...there are plenty of options out there.
One thing I've noted when buying spinach to add it to salad is that it really did not have a ton of iron in it like I thought it would since I've always heard that...apparently it has no more than other leafy green vegetables. The fact that it is "non-heme" meaning it comes from plants not from blood also means that your body only absorbs 3-8% of what you ate, and depending on how much vitamin C you are eating with it, it could be even less [iron from plants is more easily absorbed with vitamin C]. The iron in meats is better, with your body absorbing about 23% of the iron in what you consumed....but still, that is not very much iron! If you eat 3 ounces of hamburger, it only has 1.8 mg of iron, so you would only be absorbing about 0.4mg if you get 23% of it. But still you could try giving her more meat along with the other things.
As for how much she needs, I looked it up because I need to know for my son as well! :
"Children ages 1-10 generally need about 10 mg. per day of iron"
http://www.askdrsears.com/faq/fn8.asp
"The RDA for iron for both toddlers and preschoolers is ten milligrams (mg) per day"
http://www.wholesometoddlerfood.com/toddlercalcium.htm
Here is a link to Harvard's site regarding iron content in specific foods http://huhs.harvard.edu/assets/File/OurServices/Service_N...
And here is a link to the CDC's site that tells how much iron in milligrams people of different ages and genders should be getting each day:
http://www.cdc.gov/nccdphp/dnpa/nutrition/nutrition_for_e...
And one more site: http://www.keepkidshealthy.com/nutrition/iron_requirement... , which explains daily values:
"DV = Daily Value. DVs are reference numbers based on the Recommended Dietary Allowance (RDA). They were developed to help consumers determine if a food contains a lot or a little of a specific nutrient. The DV for iron is 18 milligrams (mg). The percent DV (%DV) listed on the nutrition facts panel of food labels tells adults what percentage of the DV is provided in one serving. Percent DVs are based on a 2,000 calorie diet. Your Daily Values may be higher or lower depending on your calorie needs. Foods that provide lower percentages of the DV also contribute to a healthful diet."
So based on this, one cup of Cheerios has 18 mg of iron...half a cup has 9mg. If toddlers need 10 mg it is completely doable just with eating cereal every day along with the other foods you will be feeding her