Here's a guide:
Porsche Boxster Starter Replacement - 986 / 987 (1997-08) - Pelican Parts Technical Article
It's literally step by step, showing which tools you need and which bolts you need to undo, all part by part. I've got the exact same problem as you and I'm going to do it as well, as I haven't done it before. I'm quite mechanically minded but this really doesn't seem hard at all.
If you look at that guide briefly, you'd think "Woah I can't do that?", but look at it again. Look at the photos and what it asks you to do. What wouldn't you be able to achieve in it? If you can use a ratchet, a screwdriver and a spanner, you can do this. Follow the guide and you can't go wrong
Luckily it's quite easy to reach as you can reach it from the top of your engine bay. I'd get in there bud! You'd have the satisfaction of fixing it yourself, and saving a lot of money.
I've only spent £300 on by Boxster S in my last year of ownership, because I do everything myself. That included a full set of brake discs, brake pads, exhaust gasket and a window regulator that snapped. The window regulator would have cost that alone, let alone the labour to fit it. If I took it to a garage whenever I wanted to do something to it, I'd be broke.
Go for it