I know where you're coming from, I've been there (still am, actually). I understand professional, quality materials can be expensive. I used to be cheap too, but I can assure you, if you're cheap with your materials, you will struggle with them. Guaranteed.
I've taught a number of oil painting workshops in my relatively short career and invariably there are always a few attendees who forego the materials list and bring their box of 30-year-old paints (of every imaginable obscure color and brand), worn-out brushes and less than adequate substrates. They then spend a good portion of the workshop frustrated and fighting with their supplies, constantly remarking on how they "just can't do it!". When I explain to them the importance of quality materials, they give me the usual, "they're too expensive" or "but I need to use up my old stuff first", etc., etc., etc. Blah, blah, blah.
This is a very simple piece of advice: If you wish to do professional-quality work, you MUST use professional-quality materials. Period.
So what is the starving artist, retired-hobbiest-on-a-fixed-income or frugal-extremist to do? Here are a couple of suggestions...
1st) Don't purchase your supplies from a physical store in your area. They are nearly always more expensive than their online counterparts, and additionally, you'll pay sales tax in most cases. Instead, purchase supplies online via a reputable retailer. For us oil painters, I've found that oil paints in particular are as much as 60 percent less through an online retailer versus the local art supply store near my home. For example, cadmium colors in professional-brand oil paints are expensive. My local art store charges about $35 for a 40ml tube of Holbein's cadmium yellow. Add in sales tax and I leave the store roughly $38 poorer (and a little bit angrier). This exact same tube of paint is around $19 through several online stores and I don't have to pay sales tax. Additionally, I often receive email coupons for more discounts and free shipping. Shop around online before heading to your local art materials supplier.
2nd) There are art supplies out there that are of professional quality, but have student-grade pricing. With oil paints, I can recommend Maimeri Classico Oils. They contain no fillers or waxes and have a high level of pigment. That's really the key when it comes to selecting professional-quality oil paints — no fillers and high quantities of pigment. The advice here is read the labels, do a little research and you'll likely find less expensive alternatives without sacrificing quality.
Note: Often specific colors are priced differently from brand to brand. A cobalt blue might be less expensive in one brand than another, but is of the same quality. So mix and match if you like. You might also find you prefer the performance of certain colors by certain brands over other brands — and save a few bucks as well.
Here are just some of the online retailers I purchase my materials through. If you know of others, please post them! We artists are always looking for better prices on our materials!