what you could do is pay the 100 for the cms and then agree with the webmaster to pay a maintanance fee each month of say 10 -20 pounds so that he can do the banners and photos for you that way your in control of all the stuff that is important and easy to do ie changing text, tours , prices, blogs, ect and then he is on hand for anything that you dont understand
that what i do even though yes the option to add remove my photos and banners is there on my cms i just cant be assed to do it
if you been happy with him so far and hes been ok so far in terms of reliability and getting stuff done quickly when you ask for it to be done, then a good competent webmaster is worth his weight in gold ( imo)
while there are lots of free scripts out their its still his time to add /create it to your website and if its clearly mentioned on his website that cms is a further 100 pounds then hes not ripping you off
Its quite common to do this ( pay a monthly fee) i do for my 2 websites that i have but i know that my webmaster get my photos and banners done for me straight away
otherwise you could just get a moonfruit site or free site and do it all yourself