Ammonia based windscreen washer fluid or window cleaner, (Windex), IF you can get the ammonia based stuff! I've yet to find any in the UK.
Personally I would day it's not a good thinner for acrylic, ok for cleaning the ab afterwards.
If you buy IPA in litre bottles it's not expensive, just over £10
SHL 1 Litre (1000ml) Isopropanol 99.9% (IPA) CHILD PROOF CAP | eBay