Not having any relatives around, I can honestly say I'm jealous, on the money issue alone :)
I realize it can be a double-edged sword leaving your kidlet with a relative - what if it doesn't work out and all that - but my in-laws are babysitting all their grandkids who live close by and it's working out well for all of them. I think it's because they all have the same philosophy on parenting, though.
My sister was having her kid babysat by both sets of grandparents, with varying degrees of success. She had issues with one set being too permissive and the other set allowing the kid to be too much of a tomboy. When Hanna was a baby, she was with her grandparents whenever she couldn't be with her parents - but at just under 3 years old, she started going to daycare, and my sister is much happier with that arrangement.
My own daughter, now 19 months old, is in daycare and the hardest part in the beginning was leaving her with a total stranger. That lasted for the first few weeks, but she's been going since August and we're all used to it. Dropping her off no longer makes me cry :) I know I'd have issues with both sets of grandparents, if they were close, but I think in the beginning, I'd still have preferred a family member over a total stranger.
Another thing to think about it interaction with other kids - of course, this depends on how old your baby will be when you return to work, but also on the kid's personality. Mine was the only child at her homecare place in the begining, which we thought was great. All the attention and all that, but once she started feeling at home there, she became bored all by herself. Now there's another kid there and she's much happier and loves going more than she did before.
Good luck!