If you can only afford one CP ... here's an idea!
Now, here is another idea I have used, when I was starting out, because it allows you to use one large CP-filter on all sorts of other filter-diameters (ø)
This is the SONY AF 50mm/f/1.4 (ø55mm) lens + ø55mm-62mm adapter + ø62mm-77mm adapter + ø77mm CPL filter.
So, as you can imagine, if you had the rings for your various lenses ... one large CP could do a lot of work for you. You will have to use a large lens hood for this ... as the one that came with the lens will no longer fit around this configuration. The lens hood (usually rubber) would have to screw onto the front of the ø77mm filter, in this case. Also, consider getting a ø77mm lens cap to fit and protect this filter, because this lens' normal ø55mm one will no longer fit with the oversized-filter attached.
Here is the same filter being used on the TAMRON AF 28-300mm f/3.5-6.3 Di LD Aspherical (IF) ... and using only one filter-adapter ring, the ø62-77mm.
I mean ... are we getting the picture of the $aving$ involved here? The rings are about $7-12 depending on size and whatever and you can buy them is all sort of graduations and in sets, to save a couple bucks over the individual prices.
Small Minolta filter-ring? (ø49mm)
Well, why not push it ... we are working with ø49mm lenses, right, with the older Minolta AF lenses.
So, here's the Minolta AF 50mm f/1.4 sporting the ø77mm CPL
and with an extra lens cap