My grandmother had stomach cancer and I was worried about genetics?

We don't know what type because she wasn't properly diagnosed. She was already terminal from congestive heart failure among other things and had only weeks left so she opted out of the test. My great-grandmother also had adult onset leukemia. I know some types of cancer are hereditary and wanted to get my mom a genetics/DNA test to make sure she's not at an extra risk, espHitely since she's had other problems that may put her at risk like ulcers and hiatel (sp?) hernias. I would love her to get her a full spectrum test to pick up anything else too. Especially if she's at more of a risk for lung cancer since she smokes. Around how much should this cost, and how difficult is it to set up? Note- She's almost 54 and I only want to have it done for her