You got any pictures of the interior? And what equipment do you have? Household wet vac, or just a standard vacuum?
Get some cheap microfibres, a big bowl of steaming water and a few magic sponges (you can use the Flash ones or Autoglym sell their own version as do a few other companies).
These are great for plastics, door cards and trim. Keep the sponge moist (giggidy) and work in a circular motion on any plastics. You can use these on material however they're not as effective as a wet vac or even a soft brush and soapy warm water to scrub it. Foam carpet cleaner also works well on car interiors, as does stain remover however I'd only use that on the thicker carpets rather than any suede/brushed surfaces.
Ultimately though, try to borrow a wet vac as it'll make the job so much easier, and save you doing it twice if the old by hand method doesn't give the results you need. Tool hire places often sell wet vac carpet cleaners, just make sure it's got the hand held nozzle part on it.
Also, not ideal for our weather climate but carpets and seats can be removed and pressure washed. Another option would be to use a bodyshop oven if you have a mate or know someone who'd lend you one to dry the seats/carpet etc.
Product wise, anything from the major brands is usually pretty decent - the Autoglym interior cleaner is actually one of the few products they sell that actually works well.
May also be worth googling some posts on detailingworld forum and seeing what's recommended product wise depending on the fabrics and colours your working with. :smile: