Quality end mills can be resharpened a few times. That said, one may need to adjust the diameter after sharpening as it may decrease.
Sharpening end mills is a fundamental skill taught in machining school. It requires a fair amount of machining knowledge, some math, and an appropriate mill and tools. Not something most CNCers are set up to do.
Sadly, as end mill costs have dropped the art of sharpening end mills seems to be going by the wayside. Fewer and fewer shops are willing to do the work. You’ll need to search for a shop in your country that will do the work at a reasonable price.
Resharpening (and recoating) has become something of a specialty so one has to look for shops that do this kind of work. If one is using major brand end mills (e.g. Kodiak, Niagara, Harvey Tool, Onsrud) one can ask them and they will often point you to a shop… sometimes they even do it themselves.
Be aware that resharpening is most effective in larger and more exotic end mills. The purchase cost is considerable so resharpening is a real cost savings. In times past, a resharpening would be ~50% of the purchase price… which really adds up when one is going through them often.
One of the reasons I tell people to order end mills in pairs (low use) and quads (high use) is exactly this. One needs to keep their shop/projects going while tools are being sharpened or replaced.
If you haven’t already done so, start buying coated end mills. Typically, they cost less than 50% more and last 3-5 times as long as HSS and uncoated carbide.
If you decide that a tool needs to cross Rainbow Bridge, be sure to recycle it - the steel can be reused.
Here is a good a posting about end mills and coatings:
Short version for steel: solid carbide, micron grain.
Short version for coatings: AlTiN for general use, TiB2 and ZrN for Al alloy.
Here in the states resharpening shops often have good prices for small numbers of end mills… you just have to be willing to wait for them. They batch up many smaller orders into a larger batch and process the larger batch when it makes sense. Often the wait isn’t too long.