I have a flexible brush, looks like a 2' bottle brush to run through pipes, which are about 2" or less on my Ambex. And I have some wooden sticks, a piece of 1" PVC, and a 5-in-1 paint tool for knocking crud off of the pipes before I hit them with that brush. I use another wire brush and the 5-in-1 on the squirrel cage of the exhaust fan. No solutions or sprays are used; I just prefer mechanical removal of the crud - what I fondly call roastium.
The exhaust fan is IMHO the most important part to keep clean. The 2" airways have a permanent layer of crud that's about 1/8 thick at the elbows which might increase by 1/16 when they're in need of cleaning. I don't feel like the airflow is restricted, even then, so I'd say don't worry about getting those back to pristine condition. But the squirrel cage's ability to move air is hindered much more easily.
So I don't know how dirty yours is, or what you mean by 'in need of serious cleaning'... of course you may have no way of knowing at this point, but don't assume it's as bad as you think and don't be overly concerned with something that might not impact the roasting. If you find something totally unacceptable, maybe you can find new or new-ish parts of have something fabricated.