I have the same problem with trail shoes. They seem to be more rigid than trainers (for good reason I guess). But running shoes shouldn't need breaking in - they should be good to go from the off. Breaking in relates to softening the leather in shoes, and the materials used in a running shoe won't get softer.
Unfortunately, it's not a given that the same brand will work for you in both trainers and trail shoes. I'm a Brooks advocate for my road shoes, but their trail shoes don't suit me at all. I have Asics trails (after some trial and error), but Asics road shoes DO NOT FIT!
What are yours, BTW? Light and affordable sounds attractive!
Have you tried using Vaseline? I get blisters on my toes, and always slather my toes in vaseline before a long run to prevent them. Works a treat. I'd try that to see if it helps. It should reduce the friction between your foot and the shoe.
Also, try different socks perhaps? Plenty of running socks are quite padded these days, so maybe try a different type?
One thing I definitely wouldn't do is put them in the wash. It can damage the glue and deform the shoe itself - there's a lot of 'engineering' in a trainer! Some parts of the fabric may shrink too, which will make your problem worse. I really wouldn't do it.
Missing the point slightly, but will you definitely need trail shoes for your race? Which one are you doing? It's been so dry that road shoes are good for a lot of terrain at the moment. I do almost all of my running off road (woods, tracks, footpaths) and haven't used my trails all summer, until today when I put them on as it bucketed down yesterday and I thought the woods would be muddy, but no! Should have stuck with roads.