I think it sounds low, based only on my experience of getting two bids for the tile work in my MB remodel. I would get 2-3 bids for other tile guys and then you have solid numbers to work with. If it were me I might even say, "that number sounds low, but I'm going to get 2-3 bids and then we can talk more."

The number the builder gets can be low based on his volume of work with that particular tiler. Or it could be based on a less complex layout than you've indicated and would have been raised had you gone forward with the more complex layout. Bottom line is that what is written in the contract is what you get. It doesn't matter what the real world quotes you get for the same work come out to being.

Is it reasonable to ask him to show us the details of his quote?

Only if you are on a cost plus contract. If you are a fixed cost, the only thing that really matters is the bottom line figure that you were given and you are not entitled to any of the costs behind that figure. In the end, the allowances are what the allowances are. If you want something other than what's indicated in the contract, you will pay a premium for it from whatever source.

Is it reasonable to ask him to show us the details of his quote?

let me put it this way-- if he won't, he's hiding something. Get someone else. Let me show you a sample of the kind of estimate I give to any of my customers. This is copied and pasted right off the original estimate:

Bill Vincent, DBA
Creative Ceramic & Marble
67 Portland Road
Bridgton, Maine 04009
Fax: (xxx) xxx-xxx
Cell: (xxx) xxx-xxxx
http://www.creativeceramicandmarble.com

Quote for:
MEH/ 150 Kezar Heights Road

Garage Entry

Furnish and Install Ditra.....................50.00
Install tile 20 sq. ft........................65.00*
Order 25 ft.

Front Entry

Furnish and Install Ditra....................62.50
Install Tile 25 sq. ft.......................81.25*
Order 30 ft.

Laundry Room/ � Bath

Furnish and Install Ditra....................115.00
Install tile 46 sq. ft.......................149.50*
Order 52 ft.

Upstairs Bath

Furnish and Install Ditra....................117.50
Install tile 47 sq. ft.......................152.75*
Order 55 sq. ft. (more cutting than in the laundry room�
More waste)

Master Bath

Floor

Furnish and Install Ditra.........................215.00
Install tile 86 sq. ft (diagonal).................365.50*
Order 100 ft.

Shower

Install Durock.................................119.00
Furnish and install Waterproofing..............297.50
Furnish and Install 17" Better Bench............75.00
Install Shower Pan.............................420.00
Install Wall Tile 119 sq. ft...................535.00*
Order 130 ft. of tile & 20 lin. ft. of bullnose
Install shower floor tile 14 sq. ft.............45.50*
Order 16 ft.

Fireplace Hearth................................50.00

Materials

9 sheets �" Durock..............................90.00
5 gal. Laticrete 333 liquid latex additive......81.24
4 bags Laticrete 317 thinset....................44.00
3 bags Laticrete Multipurpose thinset...........48.00
2 bags Laticrete 255 non-sag thinset............70.00
Kerdi Drain.....................................98.00
Oil Rubbed Bronze Kerdi Drain..................146.86

Garage Entry............115.00
Front Entry.............143.75
Laundry Room............264.50
Upstairs Bath...........269.50
Master Bath Floor.......580.50
Shower.................1492.50
Fireplace Hearth.........50.00
Materials...............578.10

Total..................3493.85

*NOTE- These prices for tile installation are all based on square set soldier coursing (standard grid pattern) ceramic tile, except where noted. If different pattern, or stone is used, price will change.

Yes, if you're getting estimates for a job, that level of detail in the pricing is necessary. But, if a general contractor is doing a job that you are a sub on and includes in his bid, "Ceramic tile, set on Ditra, for X, Y, Z room, $4100," that's all the OP needs to know if she is insisting on rejecting that contractor's work in favor of hiring her own.

The only thing that matters here (or EVER) is the price in writing in the contract, and that's the only credit the OP will ever be entitled to, if the GC allows the homeowner to pick and choose her own subs (most won't allow wholesale substitution like that). Just because the subsequent bids are higher than the contractor's original line item, (typical for upgrades) doesn't mean she gets a credit for the higher price. If she doesn't use the tile sub that the contractor used to bid the project, then whatever price anyone else bids for the job is up to her to pay, with only the lower number as the credit. And it doesn't matter HOW the contractor arrived at that number if a credit is being given.

What if you requested to meet with the builders tile guy and ascertained his skills & experience? If he has a portfolio of his work, references you can contact, and answers your questions well then perhaps you can use him and then there is no question of allowances.

Bill,

If you were local I would have you do my work...you seem reasonable based on these prices and also we know you are good.

Steve