Hi AwkwardSleeper,
I don’t know what size you are looking for and this will make a significant difference in the cost of a mattress but as you probably know your budget is very low and I would keep your expectations realistic because it’s very unlikely that you will be able to find a good quality mattress in your budget range.
Just in case you haven’t read it yet … the first place I would start is the mattress shopping tutorial here which has all the basic information, steps, and guidelines you will need to make the best possible choices … and know how and why to avoid the worst ones.
There is also more about the most important parts of the “value” of a mattress purchase in post #13 here that can help you make more meaningful comparisons between mattresses.
When you get to step 3 in the tutorial post … then the better options and possibilities I’m aware of in the Victoria, BC and Up Island areas (subject to the guidelines I linked about “value” in the previous line) are listed in post #2 here.
The tutorial post also includes a link to the better online options I’m aware of that will ship across Canada as well.
In your budget range it may also be worth considering a good quality futon or even a single layer of good quality polyfoam with a good cover.
There is also more about the different types of support systems that would generally be most suitable for different types of mattresses in the foundation post here.
I would also be cautious about mold and mildew in damp climates and I would avoid solid surface support systems under your mattress (see post #10 here) so that there is some airflow and ventilation under your mattress to help any moisture buildup evaporate.
Phoenix