First of all I think the consideration isn't only the cost but the amount of time it will take you to work on each application. With Optometry there is no application service like there is with Dental or Medical schools. You'll have to apply to each school seperatley. Second of all it doesn't really matter whether you apply before taking the OAT or after as long as you can get the whole process done by mid January. From what you've described I'd recommend you take the OAT before Christmas and then decide if you want to apply...you could then spend the next 2 or 3 weeks getting your applications ready and sent off. I believe it takes the schools 3 weeks or so to recieve your OAT scores (with the computerized OAT). here is more explanation/detail, if you so desire.....
I've been in this same situation and have decided to wait a year. But if your total life situation would signal a preference towards applying to and hopefully starting Opt school in 06 instead of 07 then I'll let you know what I've found out from my research and speaking to school admissions officials over the past few months. As long as you can get the test done by early-mid January you should be fine (of course every school is different but this is the general feel I've gotten). Once you hit Feb you are pushing it and March may be too late, unless of course you score really well (340 or above) and your gpa is at or above average. (It will also depend on extracurricular stuff cause that can make a candidate stand out too. I've got one friend, that is at SCO currently, that had a 3.2 GPA and didn't take the OAT till Feb (got a 310) but still got into SCO and SCCO(the only schools he applied to)...but this was likely because he had a ton of opt experience and extracurricular stuff)The reason is that most schools are on rolling admissions and have accepted 80-90% of their class by March and so their remaining slots are extremly competitive. Get the OAT study guide(
http://www.opted.org/info_oat.cfm) and see how well you know the topics and what score you might be able to acheive. Take a look (
www.opted.org) at the school profiles of entering students and compare your gpa and likely OAT (on opted.org). If you feel like you can take it by early-mid Jan and get a 320 or so and your gpa is around 3.3 then I'd say go for it for 06 entry instead of delaying as your odds will likely be good to get into a school or two in the continental U.S. There is always the Puerto Rico School (and a lot of threads loaded with information on them here on this forum

if that is an option for you and I see you may be from Canada so have you looked at those schools?
best wishes