I took a 400-level undergrad course in GR which used "Gravity" by Hartle; I thought it was a good book. With a good high-school math education I think you might be a bit underprepared, but not all that much. It doesn't emphasize the math all that strongly, but as far as I know all the important equations are contained therein.
I'm going to warn you, though, I've never heard of a treatment of GR without tensors. If you're self-teaching you won't need to solve problems with them, though, so you can probably get the concepts without being too thorough with the machinery.