I jumped right into a 21' Chieftain feet first for my first rebuild. Figured I like bigger boats much more so why start small when I can get what I want the first time.
You can see some of what you will run into and what to expect.
http://forums.iboats.com/forum/owne...4-chieftain-21-i-o-is-home-the-rebuild-begins
Also go to this page where there a bunch of Islander rebuilds, you will find the Chieftains and Starchiefs to be very similar, even exactly identical in many aspects.
http://forums.iboats.com/forum/owne...ft-rebuilds-and-restorations-they-re-all-here
Mine sat outside for 10 years uncovered that I know for sure. Surprisingly much of the floor sections weren't in bad condition but they are all getting replaced anyway. The transom was mulch though. Upholstery shot, but did come with complete camper canvas that needs to be restitched. I payed $700 not knowing for sure if the engine will run or not but seems it's the I6 and it isn't cracked I have no doubt it will run. Those old engines had a great reputation. I've had them in many trucks and a few cars, they took all the abuse I threw at them when I was young and dumb. Even had one in a '68 Nova that was locked up tight when I bought it. Freed it up over a couple weeks time with penetrating oil and she finally spun free. It smoked like mad for the first half hour burning all the penetrate out of it but after that it ran like a top. Says a lot for these I6 Chevy engines. I would assume the Islander you looked at has the same ?
Even worst case scenario you can pick up a nasty glasser donor boat with a good drive train to transplant.
Money wise, that's a tough call. All depends on how far you take it and local prices. You can get away with using a good grade of BCX ply to save money or spend more using marine grade. If you completely strip the hull it will cost quite a bit more because you need to go a different process to prime the aluminum. You can scuff the pain and just use self etching primer where aluminum shows then use regular primer over it all.
The main question for yourself is are you willing to put the effort into a big boat. The rest comes easy. With the amount of helpful information the guys here have documented and they will always jump in to answer questions and give pointers, you will feel quit confident about the rebuild.
She just needs the effort. Check out the other rebuilds. A lot of amazing results. I'm quite outta touch with new boat prices now but what's a 21' cruiser cost now, $30k ? I bet I'll have under $4k in my Chief when she's done.