hi Newmummy85
congrats on the pg =)
It is normal to put on weight! obviously, there is baby, there is amniotic fluid, there is placenta, your increase in blood volume, increase in fluid =)
change in diet too, even if you are still eating 'healthy' metabolism etc changes slightly and may be enough just to bump you over.
lifestyle changes too, you might not be as active as you once were.
just keep up regular exercise, like a 30 min walk everyday if not most, and eat your vegies and fruites etc =) look after yourself and there for your baby

things that might be an issue is gest. diabetes, even though this might not be related to your weight gain, have you had a glucose load test yet? was it normal?
also do you know what your fundal measurements are? (where they measure from your pubic bone to the top of your uterus.) if these are all normal i wouldn't worry about it.
=) hopefully that helped and maybe got others to post too.
no idea about the budget sorry =(
good luck with it!!