No one has yet asked the original poster the obvious question of what type of photography he plans to use the camera for. The three cameras he mentions, the XA, Stylus and Stylus Epic have typically been used as "carry it with me when I leave my more serious cameras at home" cameras. There are a couple points to bear in mind when using them this way. If they are used with 400 speed film (the typical all purpose speed) and are used in daylight, the maximum shutter speed will be factor. The XA and Stylus (and the rollei 35 models for that matter) all have a max shutter speed of 1/500th of a second. Daylight, 400 speed film and 1/500th are going to give you apertures around f8-f16. The maximum aperture won't matter much, so having the control over it, as with the XA, is moot point. In addition to this, just about any point and shoot with a prime lens is going to give good results with apertures in this range.
Indoors, in a room with lots of window light on a sunny day, with 400 speed film, you'll be running into the opposite issue. Even at f2.8, the shutter speed will be around 1/30-1/60. This is just fast enough to hand hold with steady hands, but if your subject moves, its not fast enough to get an un-blured image. You will generally need flash. The flash attachments or built in flashes on these cameras will give give you pretty unnatural light. I haven't found a solution to this issue when using a P&S camera. Putting these cameras on a tripod sort of defeats their purpose of being portable and easy to carry with you.
All of this is to say that the difference between a f2.8 and a f3.5 maximum aperture on these cameras is of limited value as it only comes into play in limited situations. The maximum shutter speed is probably a more important factor. The Stylus Epic at least has a 1/1000th max shutter speed.
When it comes to cost, you can haunt garage sales and thrift stores if there are any in your area and eventually you may find one of these for a few dollars. If you like to haunt these places, its worth looking. You also might find a far nicer equipment for bargain prices. I'm one of those people who like to go hunting to see what I find. I know a number of people who consider it a waste of their time. In the last 10-12 years, I've come across 3 XAs, 4 Stylus Epics and 2 Stylus' for less than $5 each, but I will stop at a couple thrift stores and/or garage/estate sales every week. If you have other uses for your time, it might be better to buy from an online source that will charge more. I think there is a greater number of online re-sellers picking up film cameras at thrift stores and garage sales than there were a few years ago. There's enough demand online to make it worth their while, so there are not as many available for the casual buyer as there where in the past.
Another poster commented that these cameras are getting too old for the electronics to be dependable. I wouldn't agree with this statement. I have dozens of electronically controlled cameras some of which are 40+ years old that still work fine. They may die suddenly, but what does it matter? I don't use them for work and if I'm suddenly without a camera when out on a walk, it really doesn't matter. When I take photographs for work, I use a current DSLR.
There are an awful lot of myths about cheap cameras that will give you the same results that a camera costing several thousands of dollars will on the web. I've tried a great many of these cameras just for fun of it. None of results from them comes close to the results and flexibility obtained with a professional system. That doesn't mean that they aren't fun to use at times.
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Southworth Run 8-30-2014 1 by Adnan, on Flickr
Mr. Moustache by Adnan, on Flickr
A pointed Tale. (and tail) by Adnan, on Flickr
