
I would be looking out for a 'cheap' flea/tick spray that contains Pyrethrins, the pet-shop sort. While these are fairly useless for normal flea control, Pyrethrins/Pyrethrums are an insect repellant, so a light misting over the dogs' legs and undercarriage before going to a tick infested place may well prevent them attaching.
Alternatively, get a small, empty plastic pump-spray bottle from Boots, add a small amount of water plus some drops of Citronella essential oil and Calendula essential oil, then spray as above. I haven't tried this myself but will do in a few months when I have a walk planned in a certain tick infested area, which myself and the dogs really love (an iron age hillfort nearby, which in late Spring has wild orchid meadows, and is the most peaceful and relaxing place I know).
I went to this area last year in May and poor doggie came home with about 6 of them. I then found an insect repellant spray with the active ingredient Pyrethum. I happened to go back to the same place a week later with a friend, used a very light misting of this on my dog's featherings and belly, and he didn't pick up any, so this year I will see if the essential oil blend will do any good (it won't do any harm, if the oils are used very sparingly and are diluted).