$450 for a conversion is a lot of money. If you can afford it then skip the following.
Wheels you can keep, just get a cog from an old cassette or a cheap Shimano BMX cog. PVC pipe works in theory, but getting it cut straight enough can be a PITA.
For cranks/BB, get a cheap
Sugino crankset, square taper. Not only is a setup like that real cheap but it also makes a great singlespeed setup. BB will last forever and is dirt cheap.
A half-link should allow you to run a magic gear. The true singlespeed experience can not be had with a chain tensioner IMO.
Sean, you misspelled 'fammily'.
Good luck,
Maurice