I would choose option 3.
Firstly, the reason for keeping the job is that you enjoy it and it gives you money to help support yourself at uni. If you quit now there is no guarantee you'll find a summer job or a replacement part-time job next year, and even if you do it may be something you hate. This seems like a big risk to take and imo not worth it.
Secondly, the reason for taking the bus is that it is the cheaper option. It would leave you with £70 + commission per week after taking off the £30 in bus fares, whereas if you got accommodation in your uni town then all the money you were making from working would be going on living. Of course this would only be the case if you couldn't get work in the week but as there's no guarantee of this I think it's best to assume you won't for now. Yes it will make the weekends long but it's only 2 days a week.
It's up to you if you try to get work in the week too, but if you do I would suggest looking for that in your hometown to make things easier for yourself. Of course it will be harder if you're not available at weekends but it's not impossible and even if you don't get anything you've still got £70 + commission coming in, and you've still got your job next year (and if you add up all the £100s from weekends at uni it will outweight the potential full time hours you could have had over the summer).