My cat red scabs and irritated skin on his underbelly and stomach

My Ninja cat has just recently been getting these reddish scabs on his stomach around his nipple area and also he has rough scabby skin on his tail base and around his neck. At first i thought it was fleas but I gave him a flea bath and also used advantage. However it didn't help and he continues to scratch and bit at his stomach. My other cat is fine but my Ninja cat is suffering and I dont get paid till the end of next week and can not take him to the vet until then. I just need some advice in the mean time what can I do to help my cat? Is it serious will he be ok until the end of the week? Here is an images please help.  

Yikes!  That looks painful!  Have you changed litter or food recently?  It could be an allergy to either of those two things.

I know my poor baby I have got this jumbo sized Tidy Cat litter from wal mart but its the same brand as before also Ive been giving him fish wet food because I thought he may need some more Omega 3s but he still eats the same dry food (purina indoor formula). Right now Im keeping him inside I usually let him out in the morning to eat grasss and I watch him the whole time. But ever since these scars started appearing Ive stopped letting him outside and am only feeding him dry food now until he gets better. 

I don't know where you are, but has the grass been treated with anything?  Could be a reaction to that. Keeping him inside forever is a great idea!  He's safer and his quality of life will be better.