If you want to build your own, Sun Ringle has 451 rims which it designates as 1-1/8 and 1-3/8. See this PDF. This seller has those two sizes shown here. The leftmost two categories. (The other categories are 406 rims.). You can get a CR-18 rim for about $25. Then get a Tiagara hub for $23. (I assume that's 100mm.).

Use the spocalc.xls spreadsheet to calculate your spokes. (Scroll all the way down that page to read how to measure the things it needs as input. The Sun PDF linked above has the ERD. For the 406 rim I recently bought, it was within a MM. I measured mine using two spokes pulled together, like the page describes.).

If your LBS doesn't have the spokes you need, you can order them custom cut here for .72 + .15 for the nipple.

I used this site's instructions to lace my spokes. It has a couple errors. I informed the owner today of the errors. There's also this site.

That puts you around $80. Call it $100 with shipping. You might find lower prices elsewhere.

I'm finishing my first wheel. It's not hard.