PLA, at $15 to $28 a kilogram. That is 1.5 to 2.8 cents a gram, and nothing else on this site starts lower.
Ranked purely on price, the order runs PLA, then ABS, high-speed PLA and PETG all at $18 to $30.
Per part, the ranking changes
Price per kilogram compares spools. Price per cubic centimetre compares parts, and density scrambles the order:
| Material | Spool price | Per cm³ of part |
|---|---|---|
| ABS | $24/kg | $0.025 |
| PLA | $22/kg | $0.027 |
| PETG | $24/kg | $0.030 |
ABS is the lighter polymer at 1.05 g/cm³ against PLA's 1.24, so the same object uses fewer grams of it. On material alone ABS is the cheapest of the three, which is not what the shelf price suggests.
Why PLA is still the right answer
Because the spool price is not the cost. ABS needs an enclosure, prints slower, and carries a much higher scrap rate — the whole-spool comparison on this site puts a kilogram of ABS at $38.01 against PLA's $30.46 once electricity, machine time and failures are counted.
The cheapest filament is the one that finishes the print. PLA prints on anything, in any room, with no drying and no enclosure, at a difficulty rating of 1.
The expensive end, for scale
PEEK runs $400 to $900 a kilogram and ULTEM $250 to $500 — twenty to thirty times PLA. PA6-CF at $60 to $120 and PPA at $90 to $180 sit between.
Those prices are not markups. They are what the polymer costs, and they are attached to properties nothing cheaper provides.
The gap also explains why nobody prototypes in them. Iterating a design in PLA and printing the final part in an engineering material is standard practice precisely because the first spool costs a twentieth of the second.
Where to actually save money
Not on the spool. On the scrap rate, the infill setting and the machine time — all three of which appear in the print cost calculator and all three of which are larger levers than the difference between a cheap PLA and an expensive one.
Rank on cost against your other requirements in the material selector.