When you have decided to re-do your bathroom you need to be realistic about your
plans and this will help you keep the costs down on a tight budget.
One thing you can do which is very cost effective is replace your bath tub with a stand up shower. For example, matki showers from roca bathrooms. This will give you more room in your bathroom.
When carrying out the work you need to think about whether you need a builder or whether you have the skills to DIY. If you have the skills, then this keeps the cost down even more. If you don't, do not try and do it anyway. You might make more mess and if you make a mistake, then you might need to pay out even more to rectify it.
Try going to your local DIY store to pick up some cheap yet durable bathroom cabinets. These can actually be very cost effective and will last years. If you fix them to the walls, then even better. This will give you more floor space. You could try and find a mirrored cupboard as well, as this will help reflect a lot of light around the room which again, creates the illusion of bigger space.
If you are replacing the tiles you can also find these in your local DIY store. Usually the cheaper ones are just as good as the more expensive ones, so don't feel like you have to pay out a lot of money.