I would suggest the GBA Expansion from the M3 team rather than an EZ 3 in 1 since there is more support from the M3 UI and Rudolph has discontinued support for his new releases for any M3 product. So unless you're okay with an old version of GBA EXPLoader, get a GBA Expansion from M3.
You can buy them from Realhotstuff.com and Dealwoot.com. I commonly use RHS, but I heard Dealwoot is good too(assuming that you live in the USA according to your flag). Dealwoot has free USPS? shipping while RHS has FedEx, USPS?, and DHL(recommend this one).