If you want cheap and adequate, use Al foil as mentioned. However, just keep in mind that Al is not as good a thermal conductor as (pure) Cu, and common Al foil is prone to wrinkling/creasing, and will result in several tiny air pockets between each wrap layer. Seeing as Al foil is verrry thin, there will be many, many layers. Not good for thermal conductivity, but certainly better than nothing at all.
If you want the best practical solution, I would recommend a slightly modified "PFlexPro" method: The first thing to do is to polish your reflector, and the bore of the P60 host.
If you have a Dremel and the applicable bits/polishing wheels, this will go a lot faster.
Then you will want to buy a sheet (NOT tape or adhesive-backed sheet) of 4 or 5 mil copper foil, preferably C110 if you can find it.
For 4-mil thick foil (.1mm), cut it into strips 12" or so long and 1/2" wide, but Leave the last 3-4" of the strip 5/8" wide.
Begin wrapping the reflector starting with the 1/2" wide end, making sure the larger section at the end of the strip is facing towards the pill/spring. Keep the wrap as tight as you can. Once near the end, the larger 5/8" section should cover the top of the spring. Then, it's just a matter of test fitting until you get the right wrap length. I usually cut off about a 1/2" at a time until I get close, than maybe 1/4" at a time. You will want it to be a tight fit, where it takes some effort to press in, but you can still screw the head down to seat the drop-in.
If you are running anything that is going to be pulling 3+ amps, I would definitely go for the latter. YMMV.