This useful forum has a comment with an idea i've been kicking around - wetting down sheets to make a swamp cooler effect: Cheap RV Living
My ex-husband and I lived in a tiny third floor walk up with no AC. We used to take our spare sheets and wet them/ wring out then hang them with a fan aimed at them - one in each room we wanted cooled down. It worked well enough for us to be comfortable.
Wearing damp socks with a fan aimed at them will also lower your body temperature. We use this method with animals who are suffering heat exhaustion. We soak their paws with alcohol. (Please do not douse your socks in alcohol and walk near any fire source - use water on your socks!)
I do like the socks idea, too. Had not thought of that. It sounds a little damply unpleasant, but if it was hot enough, it might feel great.
The same thread has a cheap recipe below that quote for making a cold pack from dish soap. Actually, it seems to be green dish soap in a baggie, with another baggie. I don't know why the dish soap has to be green. But it seems like a frugal way to make your own chillable ice packs to sleep with or sit with.